The devices at risk are the analog ones that use a copper phone line as their call path. That covers fire and burglar alarm dialers, elevator emergency phones, telecare and medical alert base stations, fax machines, dial-up card terminals, gate and entry intercoms, and the modems that report on building equipment. Some dial by themselves and some wait for a person to press a button. A device of the same kind that reports over a cellular or IP connection does not depend on the retiring analog line for its calls. Its own connection is a separate thing to check. For the analog ones there are three things to settle: whether the line is going away, whether its replacement carries the device's signals, and what powers that replacement in an outage.
\n","summary":"Analog devices that use a copper phone line as their call path are at risk: alarm dialers, elevator phones, telecare and medical alert base stations, fax machines, dial-up card terminals, entry intercoms and building monitoring modems. A device whose line is retired or moved to VoIP needs a path that carries its signals and has backup power, checked by a test arranged with the device's vendor or monitoring company.","publishedAt":"2026-08-29T16:01:24.898","verifiedAt":"2026-07-18T00:00:00","editorialStatus":"APPROVED","lastReviewedAt":"2026-10-10T03:20:20.003","nextReviewDueAt":"2026-10-18T00:00:00","templateVersion":"v2","aliases":["What devices stop working when POTS lines are retired?","Which analog devices fail on VoIP?","What legacy equipment relies on copper phone lines?","Do fire alarms work over VoIP?","Will my elevator phone work after copper retirement?","Does a medical alert system work with VoIP?","Why do fax machines fail over VoIP?","Do alarm systems work on VoIP phone lines?","What happens to POTS-connected devices during the copper sunset?","Which systems break when landlines go digital?","POTS line replacement for alarms and elevators","Devices at risk from the PSTN switch-off"],"confidenceScore":90,"confidenceLabel":"High","canonicalUrl":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"contributorOrganizationProfile":null,"contributorPerson":null,"sections":[{"id":"ee3adb06-34ab-430b-ab05-fa109792e449","sectionKey":"analog_equipment","sectionType":"markdown_section","heading":"The equipment that still sits on analog lines","introMarkdown":"The UK government's [guidance on the move to digital landlines](https://www.gov.uk/guidance/uk-transition-from-analogue-to-digital-landlines) gives a list. For homes it names alarm systems, telecare devices and fax machines. For businesses it adds \"lift alarms, burglar alarms or card payment systems.\" Telecare is the British term for the pendant and base station sold in the US as a medical alert system.\n\nCommercial buildings add a few more. Atlantech Online, a carrier that replaces copper lines in buildings, covers fire alarm panels, elevator emergency phones, intrusion panels, gate callboxes, fax machines, point-of-sale terminals and ATMs on its [POTS replacement page](https://www.atlantech.net/solutions/voice/pots-replacement). It also lists the modems that monitor HVAC systems, generators and fuel tanks. By its count, a 50,000-square-foot office building usually has six to twelve analog lines.\n\nSome of these lines run with nobody attending them, which makes them easy to overlook. The UK guidance says \"Communications providers will not know which devices are connected to their network,\" which leaves the review to the customer. Atlantech starts a replacement by walking the building to find every analog line, the device on it and the carrier that bills for it. Its page says this is the step where surprises turn up, such as a modem that no one can find or a fax line still on the bill years after the machine was unplugged.","introHtml":"The UK government's guidance on the move to digital landlines gives a list. For homes it names alarm systems, telecare devices and fax machines. For businesses it adds "lift alarms, burglar alarms or card payment systems." Telecare is the British term for the pendant and base station sold in the US as a medical alert system.
\nCommercial buildings add a few more. Atlantech Online, a carrier that replaces copper lines in buildings, covers fire alarm panels, elevator emergency phones, intrusion panels, gate callboxes, fax machines, point-of-sale terminals and ATMs on its POTS replacement page. It also lists the modems that monitor HVAC systems, generators and fuel tanks. By its count, a 50,000-square-foot office building usually has six to twelve analog lines.
\nSome of these lines run with nobody attending them, which makes them easy to overlook. The UK guidance says "Communications providers will not know which devices are connected to their network," which leaves the review to the customer. Atlantech starts a replacement by walking the building to find every analog line, the device on it and the carrier that bills for it. Its page says this is the step where surprises turn up, such as a modem that no one can find or a fax line still on the bill years after the machine was unplugged.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":10},{"id":"bf35135c-8113-4e65-b7e4-e9181d4af96d","sectionKey":"three_failure_modes","sectionType":"markdown_section","heading":"Three ways a line change can break a device","introMarkdown":"The first is that the line disappears. AT&T [said in April 2026](https://about.att.com/blogs/2026/upgrade-home-phone-and-internet.html) that it plans to retire most of its copper network by the end of 2029, with service ending in selected areas from summer 2026 after customers are notified. In the UK, Openreach [still plans to close its legacy phone network](https://www.openreach.com/news/openreach-to-protect-broadband--connections-as-pstn-closure---approaches/) on January 31, 2027. Each carrier sets its own schedule, so no single date covers every line. We cover the wider picture in whether the PSTN is still used today.\n\nA line can also go without a schedule. Atlantech describes a Washington, DC office building that lost all of its POTS lines when the local carrier's infrastructure was cut, and the carrier declined to restore them. Those lines served the elevator phones, fire alarm panels and security systems. By Atlantech's account the building went into fire watch, with extra staff on site around the clock, until replacement lines were working.\n\nThe second is signaling. A phone line was built for speech, and people cope with a clipped syllable. A fax machine or an alarm dialer sends data as sound, and the equipment at the far end has to decode it. When the line becomes a VoIP service, that sound is turned into packets and back again, and the conversion has to suit the device. Fax shows why this needs checking. Cisco's [data sheet for its VG400 analog gateway](https://www.cisco.com/c/en/us/products/collateral/unified-communications/vg-series-gateways/datasheet-c78-741973.html) documents two different ways of carrying a fax, T.38 relay and pass-through. The gateway is set up for one of them, and the choice has to match the service on the other side. So a new line that gives a clear dial tone has passed only the first test. The device still has to complete a real transmission to the far end.\n\nThe third is power. The UK guidance explains that an analog line carries a low-voltage supply from the telephone exchange, enough to run some basic corded handsets. A digital landline delivered over broadband through a router or adapter cannot carry that supply. Handsets and routers then run on the building's power and stop in a power cut unless a battery or generator backs them up. A panel or base station with its own supply and battery can keep the device itself powered. The line is a separate matter, because it now depends on equipment in your building. A router or adapter with no battery takes the line down with it, whatever powers the device behind it.","introHtml":"The first is that the line disappears. AT&T said in April 2026 that it plans to retire most of its copper network by the end of 2029, with service ending in selected areas from summer 2026 after customers are notified. In the UK, Openreach still plans to close its legacy phone network on January 31, 2027. Each carrier sets its own schedule, so no single date covers every line. We cover the wider picture in whether the PSTN is still used today.
\nA line can also go without a schedule. Atlantech describes a Washington, DC office building that lost all of its POTS lines when the local carrier's infrastructure was cut, and the carrier declined to restore them. Those lines served the elevator phones, fire alarm panels and security systems. By Atlantech's account the building went into fire watch, with extra staff on site around the clock, until replacement lines were working.
\nThe second is signaling. A phone line was built for speech, and people cope with a clipped syllable. A fax machine or an alarm dialer sends data as sound, and the equipment at the far end has to decode it. When the line becomes a VoIP service, that sound is turned into packets and back again, and the conversion has to suit the device. Fax shows why this needs checking. Cisco's data sheet for its VG400 analog gateway documents two different ways of carrying a fax, T.38 relay and pass-through. The gateway is set up for one of them, and the choice has to match the service on the other side. So a new line that gives a clear dial tone has passed only the first test. The device still has to complete a real transmission to the far end.
\nThe third is power. The UK guidance explains that an analog line carries a low-voltage supply from the telephone exchange, enough to run some basic corded handsets. A digital landline delivered over broadband through a router or adapter cannot carry that supply. Handsets and routers then run on the building's power and stop in a power cut unless a battery or generator backs them up. A panel or base station with its own supply and battery can keep the device itself powered. The line is a separate matter, because it now depends on equipment in your building. A router or adapter with no battery takes the line down with it, whatever powers the device behind it.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":20},{"id":"12dea67f-2c40-45d8-8c91-5cce2f8f620b","sectionKey":"device_dependencies","sectionType":"table_section","heading":"What each device depends on","introMarkdown":null,"introHtml":null,"outroMarkdown":null,"outroHtml":null,"contentJson":{"rows":[{"cells":["Fire or burglar alarm dialer","A call path that delivers the panel's signals to the monitoring station","Alarm company and monitoring station"]},{"cells":["Elevator emergency phone","Two-way voice from the cab to someone who answers","Elevator contractor and the answering service"]},{"cells":["Telecare or medical alert base station","A phone jack on a service the unit is rated for","Device provider"]},{"cells":["Fax machine","A fax mode the new service supports","Phone service provider, then a test page each way"]},{"cells":["Dial-up card terminal or ATM","A data call that completes","Payment processor or terminal supplier"]},{"cells":["Gate callbox or entry intercom","Dial tone and a number that answers","Installer or phone service provider"]},{"cells":["Building monitoring modem","A data call to the monitoring service","Equipment vendor"]}],"columns":["Device","What it needs from the line","Who confirms the replacement"]},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":30},{"id":"d3d83a65-fb9c-4944-9456-fd14df1b4794","sectionKey":"lower_risk","sectionType":"markdown_section","heading":"Where the risk is lower","introMarkdown":"Ordinary phones are the simpler case. The UK guidance expects the change to be straightforward for most consumers and businesses. A person on a call notices a problem and says so, which a dialer in a closet cannot do. The power change still applies to them. A basic corded phone that ran on the line's own power stops working in a power cut once the line arrives through a router, unless that equipment has a battery.\n\nEquipment that reports another way has less at stake. A fire panel with a cellular communicator, or a card terminal on the office network, does not place its calls over the analog line that is being retired. That holds only while its own connection stays up, so check two things. An IP device may run on broadband that arrives over the same copper. Some panels also keep an analog line as a fallback path.\n\nAn analog device is not automatically stranded either. Bay Alarm Medical's [guide to compatible phone services](https://www.bayalarmmedical.com/medical-alert-blog/medical-alert-system-compatible-phone-service-providers/) tells customers with VoIP or cable phone service to look for systems labeled as compatible with \"digital phone service.\" It also describes the case that does not work. Its base station plugs into a phone jack, so a home phone that reaches the modem only over Wi-Fi gives the unit nothing to connect to. For that home, Bay Alarm points to its base station with a built-in cellular connection. That is one vendor describing its own equipment. For this unit, the answer came from the company that supplies it.","introHtml":"Ordinary phones are the simpler case. The UK guidance expects the change to be straightforward for most consumers and businesses. A person on a call notices a problem and says so, which a dialer in a closet cannot do. The power change still applies to them. A basic corded phone that ran on the line's own power stops working in a power cut once the line arrives through a router, unless that equipment has a battery.
\nEquipment that reports another way has less at stake. A fire panel with a cellular communicator, or a card terminal on the office network, does not place its calls over the analog line that is being retired. That holds only while its own connection stays up, so check two things. An IP device may run on broadband that arrives over the same copper. Some panels also keep an analog line as a fallback path.
\nAn analog device is not automatically stranded either. Bay Alarm Medical's guide to compatible phone services tells customers with VoIP or cable phone service to look for systems labeled as compatible with "digital phone service." It also describes the case that does not work. Its base station plugs into a phone jack, so a home phone that reaches the modem only over Wi-Fi gives the unit nothing to connect to. For that home, Bay Alarm points to its base station with a built-in cellular connection. That is one vendor describing its own equipment. For this unit, the answer came from the company that supplies it.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":40},{"id":"8245d516-d659-4735-a705-2c7b09ae1d6a","sectionKey":"replace_device_or_line","sectionType":"markdown_section","heading":"Replace the device or replace the line","introMarkdown":"Each analog device leaves you two choices. You can replace it with a version that reports over cellular or IP. The UK guidance advises checking that a new alarm or device works with VoIP services or can connect to a mobile service such as 4G. Or you can keep the device and give it a line that behaves like the old one.\n\nAtlantech's POTS replacement is an example of the second choice. Each analog line moves to an FXS port on an appliance in the telecom closet, so the device is still given an analog line with dial tone. Our answer on [PSTN gateways and FXS and FXO ports](https://www.answerstack.io/q/what-is-a-pstn-gateway-and-what-do-fxs-and-fxo-ports-do) explains that port. The appliance sends calls over broadband, with 4G LTE as a second path, and Atlantech lists a battery that runs up to 24 hours. One unit handles two to eight lines. The page gives a typical cost of $15 to $45 per line per month plus hardware. Actual pricing is by quote and depends on line count, connectivity and installation.\n\nSuppose a four-story medical office has four copper lines: a fire alarm panel, an elevator phone, a fax machine and a card terminal at the front desk. The payment processor offers a terminal that uses the office network, so that line is cancelled and never replaced. Assume the alarm company and the elevator contractor confirm that the fire panel and the elevator phone are compatible with an analog replacement line. Those two move to ports on an appliance with a battery and cellular backup, and each passes a test arranged with its monitoring center. The fax machine moves to the same appliance, set to the fax mode the service supports, and it sends and receives a test page.","introHtml":"Each analog device leaves you two choices. You can replace it with a version that reports over cellular or IP. The UK guidance advises checking that a new alarm or device works with VoIP services or can connect to a mobile service such as 4G. Or you can keep the device and give it a line that behaves like the old one.
\nAtlantech's POTS replacement is an example of the second choice. Each analog line moves to an FXS port on an appliance in the telecom closet, so the device is still given an analog line with dial tone. Our answer on PSTN gateways and FXS and FXO ports explains that port. The appliance sends calls over broadband, with 4G LTE as a second path, and Atlantech lists a battery that runs up to 24 hours. One unit handles two to eight lines. The page gives a typical cost of $15 to $45 per line per month plus hardware. Actual pricing is by quote and depends on line count, connectivity and installation.
\nSuppose a four-story medical office has four copper lines: a fire alarm panel, an elevator phone, a fax machine and a card terminal at the front desk. The payment processor offers a terminal that uses the office network, so that line is cancelled and never replaced. Assume the alarm company and the elevator contractor confirm that the fire panel and the elevator phone are compatible with an analog replacement line. Those two move to ports on an appliance with a battery and cellular backup, and each passes a test arranged with its monitoring center. The fax machine moves to the same appliance, set to the fax mode the service supports, and it sends and receives a test page.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":50},{"id":"7161b7b8-a12f-4d24-86a4-244acc8929c5","sectionKey":"signal_path_test","sectionType":"markdown_section","heading":"Testing the signal path","introMarkdown":"A dial tone does not show that a device's signals arrive, so each device needs a test of its real job across the new line. Atlantech's cutover process says \"fire and elevator lines are tested end-to-end with the monitoring center after each cut.\" Hold any replacement to that standard, whoever supplies it. A fax machine gets the same treatment, with a test page sent and a test page received.\n\nArrange the test with the alarm company or elevator contractor beforehand, so the monitoring station expects the signal and logs it as a test. A station that receives an unannounced alarm signal can treat it as a real emergency.\n\nA passed test shows that the signal path worked on that occasion. The battery and the backup connection need their own checks.\n\nFire alarm and elevator lines can also carry approval requirements that depend on where the building is. Ask the alarm company or elevator contractor to identify which approvals apply to yours. Where any do, get the new path approved before you cancel the copper line, and keep that line in service until every device on it has passed its test.","introHtml":"A dial tone does not show that a device's signals arrive, so each device needs a test of its real job across the new line. Atlantech's cutover process says "fire and elevator lines are tested end-to-end with the monitoring center after each cut." Hold any replacement to that standard, whoever supplies it. A fax machine gets the same treatment, with a test page sent and a test page received.
\nArrange the test with the alarm company or elevator contractor beforehand, so the monitoring station expects the signal and logs it as a test. A station that receives an unannounced alarm signal can treat it as a real emergency.
\nA passed test shows that the signal path worked on that occasion. The battery and the backup connection need their own checks.
\nFire alarm and elevator lines can also carry approval requirements that depend on where the building is. Ask the alarm company or elevator contractor to identify which approvals apply to yours. Where any do, get the new path approved before you cancel the copper line, and keep that line in service until every device on it has passed its test.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":60}],"citations":[{"title":"PSTN (public switched telephone network)","url":"https://www.techtarget.com/searchnetworking/definition/PSTN","excerpt":"Telecommunications providers are transitioning from PSTN to all-IP communications.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"PSTN as circuit-switched networks that reserve a dedicated path per call; providers transitioning from PSTN to all-IP; voice phones migrate to VoIP without special work","domain":"techtarget.com","publisherName":"Informa TechTarget"},{"title":"Plain old telephone service","url":"https://en.wikipedia.org/wiki/Plain_old_telephone_service","excerpt":"supplied by a power conversion system in the central office ... a bank of batteries, resulting in continuation of service during interruption of power to the customer.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"POTS is analog voice service over copper loops; the subscriber loop is powered from the central office, which includes batteries, so service continues during a customer power interruption","domain":"en.wikipedia.org","publisherName":"Wikipedia"},{"title":"POTS line replacement: why property managers and building owners must take action now","url":"https://www.atlantech.net/blog/pots-line-replacement","excerpt":"Fire alarm panels, Elevator emergency phones, Entry/intercom systems, Security alarms, Fax lines for regulatory communication.","quoteText":null,"sourceRole":"SUPPORTING","verifiedAt":"2026-07-18T00:00:00","supportsText":"Lists legacy devices at risk on POTS lines (fire alarm panels, elevator emergency phones, entry/intercom systems, security alarms, fax lines) and frames them as life-safety systems governed by codes; corroborates claims also supported by primary or independent sources","domain":"atlantech.net","publisherName":"Atlantech Online"},{"title":"Fire alarm communicator: DACT, IP, and cellular transmission","url":"https://www.lifesafetywiki.com/wiki/fa-communicator","excerpt":"many building owners find the carrier has quietly migrated them to a VoIP or 'managed voice' service, which does not meet NFPA 72 supervision requirements.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"A DACT dials two dedicated telephone lines under NFPA 72 supervision and signals trouble if a line fails; carriers are sunsetting copper and often migrate owners to VoIP or managed voice that does not meet NFPA 72 supervision, causing uncleared trouble signals; VoIP is not acceptable for fire alarm ","domain":"lifesafetywiki.com","publisherName":"Life Safety Wiki"},{"title":"Navigating the transition from POTS to VoIP: what you need to know for your fire alarm and security systems","url":"https://preventiasecurity.com/blog/navigating-the-transition-from-pots-to-voip-what-you-need-to-know-for-your-fire-alarm-security-systems/","excerpt":"VoIP can alter the format of alarm signals, making them unrecognizable to monitoring centers.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"VoIP can alter the format of alarm signals so they are unrecognizable to monitoring centers; analog signals may not be processed correctly once converted to packets, so alarm signals can fail to reach the station; VoIP depends on electricity and internet unlike POTS powered by the network; remedies ","domain":"preventiasecurity.com","publisherName":"Preventia Security"},{"title":"Elevator emergency phones after copper retirement","url":"https://dataremote.com/elevator-emergency-phones-after-copper/","excerpt":"the carrier retiring your copper doesn't retire your code obligation.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"ASME A17.1 requires two-way communication between the car and a monitoring location regardless of line technology; elevator phones traditionally rode on copper POTS lines; the system must automatically verify the line at least once a day; copper retirement does not remove the building's code obligat","domain":"dataremote.com","publisherName":"DataRemote"},{"title":"Medical alert system compatible phone service providers","url":"https://www.bayalarmmedical.com/medical-alert-blog/medical-alert-system-compatible-phone-service-providers/","excerpt":"Because analog lines are generally less prone to signal drops than cellular or internet-based services, they are often considered a dependable choice for emergency response equipment.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"Most in-home medical alert (PERS) systems were designed around a standard analog landline; analog lines are less prone to signal drops than cellular or internet-based services; VoIP units must be labeled compatible with digital phone service; a standalone cellular base station is an alternative when","domain":"bayalarmmedical.com","publisherName":"Bay Alarm Medical"},{"title":"ITU-T T.38: Procedures for real-time Group 3 facsimile communication over IP networks","url":"https://www.itu.int/rec/T-REC-T.38/en","excerpt":"Procedures for real-time Group 3 facsimile communication over IP networks. Status: In force.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-07-18T00:00:00","supportsText":"T.38 defines procedures for real-time Group 3 facsimile communication over IP networks; in force; the recognized method for carrying fax across packet networks","domain":"itu.int","publisherName":"International Telecommunication Union (ITU-T)"},{"title":"Why faxes fail over VoIP and how T.38 fixes it","url":"https://www.ictfax.org/why-faxes-fail-over-voip-and-how-t38-fixes-it/","excerpt":"A dropped or late packet is a momentary blip in speech. In a fax transmission it is a hole in the data, and fax has almost no tolerance for holes.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"Lossy codecs such as G.729 discard detail that is the fax signal, so fax data arrives mangled; a dropped or late packet is a hole in the data and fax has almost no tolerance for holes; G.711 pass-through is brittle and breaks when conditions degrade; T.38 carries the fax data itself with fax-aware r","domain":"ictfax.org","publisherName":"ICTFAX"},{"title":"Final copper sunset: FCC, AT&T and Lumen accelerate the end of POTS","url":"https://www.mettel.net/blog/pots-lines-going-away/","excerpt":"safety-critical systems, like elevator phones, fire alarm panels, fax machines, and point-of-sale devices.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-07-18T00:00:00","supportsText":"Safety-critical systems including elevator phones, fire alarm panels, fax machines, point-of-sale devices, burglar alarms and other critical communication systems rely on POTS; traditional fax machines and dial-up internet access still use POTS; carriers are retiring copper and the notice before a c","domain":"mettel.net","publisherName":"MetTel"},{"title":"UK transition from analogue to digital landlines","url":"https://www.gov.uk/guidance/uk-transition-from-analogue-to-digital-landlines","excerpt":"Digital landlines cannot carry a power connection, which means handsets and routers must be powered from your home power supply, and they will not function in a power cut unless you have a backup power system such as a battery or generator.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-07-18T00:00:00","supportsText":"Analog networks have reached the end of their serviceable life and are moving to VoIP with most customers transitioning by January 2027; telecare devices, alarm systems and fax machines may need upgrading or a battery and network backup; digital landlines cannot carry power and will not work in a po","domain":"gov.uk","publisherName":"GOV.UK"}],"revisions":[{"revisedAt":"2026-07-20T16:01:24.898+00:00","versionLabel":"Originally published","note":"","reviewedBy":null}],"relatedAnswers":[{"id":"64a64f8a-a710-4a70-b21b-292c1eb247b6","slug":"what-is-the-pstn-public-switched-telephone-network","question":"What is the PSTN (Public Switched Telephone Network)?","publishedAt":"2026-09-23T15:17:01.345","confidenceScore":93,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"pstn","label":"PSTN","description":"The public switched telephone network: how it works, POTS retirement, and the move to VoIP.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"The PSTN is the combined telephone networks of the world's carriers, connected so that a number on one can be dialed from another. No single company owns it. Landline and mobile carriers both belong to it, and a shared numbering system holds it together. It began with copper lines and circuit switches, and parts of it now run on IP.","url":"/q/what-is-the-pstn-public-switched-telephone-network"},{"id":"ef14e83f-e61d-4263-80d2-b759e8ba8101","slug":"what-is-the-difference-between-pstn-and-pbx","question":"What is the difference between PSTN and PBX?","publishedAt":"2026-09-19T15:32:04.773","confidenceScore":93,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"pstn","label":"PSTN","description":"The public switched telephone network: how it works, POTS retirement, and the move to VoIP.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"The PSTN is the public telephone network that connects phone numbers across carriers. A PBX is one organization's own phone system, which gives users extensions and controls how calls are routed. A business normally uses both: the PBX handles calls inside the organization, and a PSTN connection carries calls to and from outside phone numbers.","url":"/q/what-is-the-difference-between-pstn-and-pbx"},{"id":"69048737-9759-4922-93ff-0af08871c2af","slug":"how-does-the-pstn-work","question":"How does the PSTN work?","publishedAt":"2026-07-18T15:31:57.455","confidenceScore":92,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"pstn","label":"PSTN","description":"The public switched telephone network: how it works, POTS retirement, and the move to VoIP.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"The PSTN connects a call in two layers. Signaling messages pass between switches to find the dialed number and ring it, and a voice path stays open until someone hangs up. On older parts of the network that path is a reserved 64 kbit/s circuit. On newer parts it is IP packets, and gateways convert between the two where a call passes from one kind of network to the other.","url":"/q/how-does-the-pstn-work"},{"id":"3cc4d7a6-6aed-4446-8dd8-13e022c3e1ba","slug":"is-pstn-secure-and-can-pstn-calls-be-encrypted","question":"Is PSTN secure, and can PSTN calls be encrypted?","publishedAt":"2026-07-11T16:01:27.137","confidenceScore":80,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"pstn","label":"PSTN","description":"The public switched telephone network: how it works, POTS retirement, and the move to VoIP.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"The PSTN gives a call no end-to-end encryption. Its security rests on how each carrier on the path protects its own network, which a caller can't see. Individual legs can be encrypted, such as the IP leg between a phone or app and its provider, but each protection runs between two devices that share the keys and ends at the device that decrypts the call to pass it on. End-to-end encryption needs compatible equipment or software at both ends.","url":"/q/is-pstn-secure-and-can-pstn-calls-be-encrypted"}],"contributorStats":{"verifiedAnswers":149,"openDisputes":0},"schemaJson":{"@context":"https://schema.org","@type":"Question","name":"Which legacy devices are still at risk when PSTN/POTS lines are retired or moved to VoIP?","text":"Which legacy devices are still at risk when PSTN/POTS lines are retired or moved to VoIP?","url":"https://www.answerstack.io/q/which-legacy-devices-are-still-at-risk-when-pstn-pots-lines-are-retired-or","answerCount":1,"datePublished":"2026-08-29T16:01:24.898","about":[{"@type":"Thing","name":"PSTN"},{"@type":"Thing","name":"Telecommunications"}],"acceptedAnswer":{"@type":"Answer","text":"The devices at risk are the analog ones that use a copper phone line as their call path. That covers fire and burglar alarm dialers, elevator emergency phones, telecare and medical alert base stations, fax machines, dial-up card terminals, gate and entry intercoms, and the modems that report on building equipment. Some dial by themselves and some wait for a person to press a button. A device of the same kind that reports over a cellular or IP connection does not depend on the retiring analog line for its calls. Its own connection is a separate thing to check. For the analog ones there are three things to settle: whether the line is going away, whether its replacement carries the device's signals, and what powers that replacement in an outage.","url":"https://www.answerstack.io/q/which-legacy-devices-are-still-at-risk-when-pstn-pots-lines-are-retired-or","upvoteCount":0,"datePublished":"2026-08-29T16:01:24.898","dateModified":"2026-07-18T00:00:00","citation":[{"@type":"CreativeWork","name":"PSTN (public switched telephone network)","url":"https://www.techtarget.com/searchnetworking/definition/PSTN"},{"@type":"CreativeWork","name":"Plain old telephone service","url":"https://en.wikipedia.org/wiki/Plain_old_telephone_service"},{"@type":"CreativeWork","name":"POTS line replacement: why property managers and building owners must take action now","url":"https://www.atlantech.net/blog/pots-line-replacement"},{"@type":"CreativeWork","name":"Fire alarm communicator: DACT, IP, and cellular transmission","url":"https://www.lifesafetywiki.com/wiki/fa-communicator"},{"@type":"CreativeWork","name":"Navigating the transition from POTS to VoIP: what you need to know for your fire alarm and security systems","url":"https://preventiasecurity.com/blog/navigating-the-transition-from-pots-to-voip-what-you-need-to-know-for-your-fire-alarm-security-systems/"},{"@type":"CreativeWork","name":"Elevator emergency phones after copper retirement","url":"https://dataremote.com/elevator-emergency-phones-after-copper/"},{"@type":"CreativeWork","name":"Medical alert system compatible phone service providers","url":"https://www.bayalarmmedical.com/medical-alert-blog/medical-alert-system-compatible-phone-service-providers/"},{"@type":"CreativeWork","name":"ITU-T T.38: Procedures for real-time Group 3 facsimile communication over IP networks","url":"https://www.itu.int/rec/T-REC-T.38/en"},{"@type":"CreativeWork","name":"Why faxes fail over VoIP and how T.38 fixes it","url":"https://www.ictfax.org/why-faxes-fail-over-voip-and-how-t38-fixes-it/"},{"@type":"CreativeWork","name":"Final copper sunset: FCC, AT&T and Lumen accelerate the end of POTS","url":"https://www.mettel.net/blog/pots-lines-going-away/"},{"@type":"CreativeWork","name":"UK transition from analogue to digital landlines","url":"https://www.gov.uk/guidance/uk-transition-from-analogue-to-digital-landlines"}]}}}