How does UCaaS compare to on-premises PBX?

A PBX is the switch that sends a call to the right extension and connects it to an outside line. With an on-premises PBX, that switch is a box or a server at your site. AT&T's comparison of cloud and on-premises phone systems describes the owned case plainly. When you own the system, you're responsible for the setup, the hardware, the security and the maintenance.

UCaaS moves the switch out of the building. Atlantech Online describes its hosted phone system in those terms: the PBX sits on Atlantech's cloud and not in the office. Your desk phones and apps reach it over a data connection to the provider, and the provider keeps the platform running. You still decide how calls route, who has which extension and what callers hear after hours. You make those changes in the provider's system, and the PBX hardware is the provider's to patch and replace. The phones on the desks and the office network are still yours.

The other difference is scope. A traditional PBX is first a voice system. UCaaS puts calling beside the other ways a team talks. Atlantech's page lists VoIP, video and chat together, with mobile apps for Android and iOS that take business calls away from the desk.

UCaaS is a subscription, so the cost is the number of users times a monthly rate. Atlantech publishes two starting rates. Its Business Line starts at $12 per user per month and lists calling features with unlimited local and domestic long-distance calling. Its Premium Line starts at $18 and lists voicemail, conferencing, collaboration and a softphone.

Suppose 40 people all take the Premium Line and the quote comes in at the starting rate. Forty users at $18 is $720 a month, or $8,640 over twelve months. That figure is the subscription alone, and the quote settles the term, setup and phones. The per-user price is only one part of a UCaaS bill.

A PBX you buy outright has a different shape. There's a large purchase at the start, then smaller recurring costs: a support contract, carrier lines or SIP trunks, licenses and the time of whoever administers it. AT&T describes the same split as a capital investment with ongoing costs on one side and an operating expense on the other. Some PBX systems are licensed or sold by subscription, which spreads the purchase out, so the example here assumes one that was bought.

The purchase is where comparisons go wrong. If you're buying a new PBX, its price belongs in the comparison. If you bought one years ago, that money is spent whichever way you decide, so leave it out. Suppose your paid-off PBX costs $7,000 a year in support, trunks and licenses. The comparison is $7,000 against $8,640, plus what each number leaves out. The PBX figure leaves out staff time and the replacement you'll face one day. The UCaaS figure leaves out phones, setup and taxes.

On those assumed numbers, the paid-off PBX has the lower recurring cost on paper. Whether it's cheaper to keep depends on the staff time and the replacement that the $7,000 leaves out. The comparison moves toward UCaaS when the PBX needs a major upgrade or its maker stops supporting it, because the purchase comes back into the sum. AT&T adds that skilled on-premises technicians and the right parts are getting harder to find, which raises the cost of keeping older equipment running.

Suppose an office reaches its UCaaS provider over a single internet connection. Every call from a desk phone there crosses that connection, so if it fails, or if the office loses power and its network equipment has no backup, those phones lose the phone system. People with the mobile app and a working connection of their own can keep taking calls. A weak connection shows up sooner than a failed one, as choppy audio and dropped calls.

An on-premises PBX has a different exposure. Calls between extensions stay inside the building, so an internet outage doesn't have to stop them. Outside calls ride on a carrier line or a SIP trunk, and a SIP trunk that arrives over the office internet connection fails when that connection does. The dependency moves to the PBX and the power that feeds it. Unless the system was installed with a redundant unit and backup power, a hardware fault or a power cut at the site takes the phones down with it.

Some cloud providers sell a local fallback that narrows the gap. Cisco's site survivability for Webex Calling uses a router on the office network as a gateway. If the site loses its connection to Webex, the phones register to that gateway for basic calling. Outside calls and E911 calls in that mode need a local phone circuit or SIP trunk on the gateway.

Remote work shows the difference in daily use. A UCaaS app works wherever its user has an internet connection. A PBX can serve people outside the building too, but your team has to build and maintain that access. Either way, each remote worker needs a setup of their own, including an emergency address that matches where they work.

With an on-premises PBX, you hold the hardware and whatever is stored on it, such as voicemail and call records. AT&T says a company that requires strict security or data storage can get greater control from an on-premises system. With UCaaS, that data sits on the provider's systems, and the contract and the account settings decide where it's kept and who can reach it.

Neither arrangement is safe or exposed just because of where the switch sits. Safety depends on who can log in, how remote access is set up and whether updates get applied. On a PBX those jobs are yours. On UCaaS the provider handles the platform and you handle the accounts.

The choice doesn't have to be replace or keep. Atlantech's business phone service sells both arrangements. You can connect to its cloud PBX, or keep your own PBX and have service delivered to it by SIP, PRI or analog. Its UCaaS page describes a middle step as well. SIP trunking extends a softphone to PBX users, so the business gets unified communications without paying to change its existing equipment until the time is right.

So a company with a sound PBX could keep it at the main office and feed it with a SIP trunk, then add softphones for the people who travel. When the PBX reaches the end of its supported life, the company can move those users to the hosted system.