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RTT (Real-Time Text)

RTT is a 911-mandated successor to TTY for hearing- and speech-impaired users. Characters appear letter-by-letter as you type, like a chat, instead of waiting for a full message. Available on iPhone XS+ and most Android phones since 2019.

RTT (Real-Time Text) is a cellular text-communication standard designed for hearing- and speech-impaired users. Unlike SMS or iMessage where the recipient sees only the completed message, RTT transmits each character as it’s typed — the recipient sees the conversation unfold letter-by-letter, similar to a Linux talk session.

Why it replaced TTY

TTY (Teletypewriter) was the legacy standard, dating to the 1960s. It used Baudot-coded tones over the voice channel at very low bit rates and required dedicated TTY hardware or special phone settings. The FCC mandated in 2017 that all US wireless carriers support RTT and migrate away from TTY by 2024.

RTT advantages:

  • Native to the phone. No external TTY device required — the phone’s touchscreen keyboard works.
  • Letter-by-letter transmission. The conversation flows naturally; you can interrupt the other party mid-sentence.
  • Compatible with 911. RTT calls to 911 connect to dispatcher consoles that show the typed text in real-time.
  • Works alongside voice. RTT and voice can be used simultaneously on the same call — useful when one party can speak and the other types.

How to enable

iPhone: Settings → Accessibility → RTT/TTY. Turn on "Software RTT/TTY" and optionally "Hardware TTY" if you have legacy gear. Once enabled, every call has an RTT button.

Android: Phone app → Settings → Accessibility → RTT call. "Visible during calls" or "Always visible" depending on preference.

Carrier and phone support

All US carriers (Verizon, T-Mobile, AT&T, Dish/Boost, plus all major MVNOs) support RTT on their networks. iPhone XS / 11 / SE2 onward and most Android flagships from 2018+ have RTT built in.

Related terms in Calling, messaging & Wi-Fi

RCS
RCS (Rich Communication Services) is the modern texting standard that replaces SMS with iMessage-like features: typing indicators, read receipts, high-res photos. Now supported across iPhone and Android.
Visual voicemail
Visual voicemail displays your voicemails as a list with playback, transcription, and delete controls — without dialing in to a voicemail box. Standard on iPhone and most modern Android since the late 2000s; some carrier/MVNO combos still have gaps.
MMS (Multimedia Messaging Service)
MMS is the standard for sending pictures, video, audio, and group texts over cellular. Routes differently from SMS through a carrier MMSC server. Increasingly being replaced by RCS on Android and iMessage on iPhone, but still the universal fallback.

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