Which communication channels and features can CPaaS add to an application?

SMS reaches any phone with text service and asks the recipient to install nothing, so it suits order alerts and reminders. Twilio's US price list charges $0.0083 per SMS segment and $0.022 for an outbound MMS. Carriers add per-message fees on top, such as $0.0035 for an outbound SMS to AT&T. Before a US 10-digit number can send application traffic, Twilio's 10DLC documentation says the sender must register a brand and a campaign.

Adding texting doesn't always mean building it. Atlantech's atlantech|text puts SMS and MMS into Microsoft Teams, on the direct-dial number an employee already has, starting at $10 per number per month. Nobody writes code, because the channel is added to an app staff already use. CPaaS is the route when the texts have to come from software your team develops or extends. We explain that distinction in what CPaaS is.

RCS makes the text interactive. Twilio's RCS documentation describes a branded sender profile in place of a phone number, up to 11 suggested replies, cards that can be sent together as a carousel, and delivery and read receipts.

Suppose a furniture store texts a customer a delivery window. Over SMS, the customer has to type an answer. Over RCS, the message arrives under the store's name with buttons for confirming or rescheduling. The store also gets delivery and read receipts.

RCS doesn't reach every customer. Twilio lists Android and iOS 18 devices as compatible. Its RCS onboarding guide adds that carriers must approve the sender and that not all phone numbers can receive RCS messages. Twilio's Messaging Services send by SMS or MMS when an RCS message fails or the carrier doesn't support it, so the store can still send those customers the delivery window by SMS.

WhatsApp reaches people inside an app they already use. Twilio sends WhatsApp messages through the same messaging API as SMS, with the address written as whatsapp: followed by the phone number. A customer's WhatsApp message arrives at the application's webhook in the same format as an incoming text. So a store that already handles SMS replies can reuse most of that code.

The rules differ from SMS in one way that shapes the design. WhatsApp requires a notification the business starts to use a template registered in advance. Free-form messages are allowed inside a customer service window, which lasts 24 hours after the customer's most recent message. So the furniture store's delivery notice goes out as a template. If the customer answers, the store can reply in its own words for the next 24 hours.

Phone calls come in two layers. The first is the call itself. Twilio's voice API places an outbound call with one request to its Calls resource. The second is control over what happens during the call, and that layer is what makes a call programmable.

Twilio's voice instructions show what that control looks like. Its verbs include Say, Play, Dial and Record, and a call can prompt the caller for keypad input. So a caller to the furniture store could key in an order number. The store's application looks it up, and the call reads back the delivery date or dials the store. Your code makes each of those choices while the call is in progress, as we describe in how CPaaS works.

Calls are billed by the minute. Twilio's pay-as-you-go US voice prices are $0.0085 per minute for an inbound call to a local number and $0.0140 per minute for an outbound local call. The local number rents for $1.15 a month.

A conversation doesn't always need a phone number. Twilio has client-side SDKs for voice, video and conversations that run in a browser or phone app, each signed in with an access token. The customer talks from your website or app without dialing a number, and the provider's infrastructure carries the call. Twilio's voice price list charges $0.0040 per minute for the browser or app leg of a voice call.

Suppose the furniture store's customer opens the store's website and starts a video call to show a damaged table leg. The store's developers build the call screen with the provider's SDK, and the store's server issues each user a short-lived token to sign in. We cover that in how CPaaS APIs authenticate requests and report events.

CPaaS email is for mail an application sends. For the furniture store, that means the order confirmation and the delivery-day notice.

Twilio SendGrid posts event data to the application, and its event reference sorts those events into two groups. Delivery events describe the message's path to the receiving mail server. Processed means SendGrid accepted the message, and delivered means the receiving server accepted it. Deferred means the receiving server rejected it temporarily. Bounce means the receiving server doesn't accept mail sent to that recipient. Engagement events report what was recorded for the recipient, such as an open, a click, a spam report or an unsubscribe.

The two groups answer different questions, so the store's application should handle them differently. A bounce on the order confirmation tells the store that message was not accepted, so the delivery notice may need another channel the customer has agreed to. A delivered event says the receiving server accepted the message. Whether an open was recorded is a separate event. An unsubscribe is an instruction, so the application has to store it against the customer before the next send.

Some features belong to one channel. Call recording and phone menus are built from the Record instruction and keypad prompts described above. Other features use several channels, and verification is the common one. Twilio's Verify confirms a user through SMS, voice, email, WhatsApp, an authenticator code, push, passkeys or silent network authentication. A login flow can offer a code by text and fall back to a call or an email through the same API.

A provider's list of channels is not fixed. Microsoft announced on September 23, 2026 that it is retiring Azure Communication Services as a standalone offering on September 30, 2028, and its SMS, email, chat and WhatsApp messaging services end on that date. A channel's reach changes too, as RCS shows.

So check the provider's current list before you design around a channel. It also helps to store each customer under your own ID, with the phone number, WhatsApp address and email address as attributes of that record. When a customer changes a number or a provider drops a channel, you update how you reach that customer, and the history stays attached to the same record.