TTY mode on phone: What it means and how to use it

TTY or teletypewriter is a mode of real-time communication that was originally designed to help people with hearing impairments communicate over regular voice lines. These include traditional landline voice calls, as well as the voice calls we make with modern smartphones.

Essentially, you initiate a voice call as you normally would, then you use a hardware or software TTY device to type your message. This message is transmitted as a pattern of audio tones (which sound like beeps) that are then received and interpreted by the receiving device, which also has TTY enabled. Similar in nature to Morse code, these audio tones generally follow the Baudot code, a system where characters – letters and numbers – are encoded into distinct audio tones. The Baudot code was used in the 1870s to transmit messages over telegraph.

Why can’t we just use WhatsApp?

You can of course simply send a text via a messaging app like WhatsApp, or even a more traditional SMS, which is why TTY isn’t commonly used these days. The main difference between TTY and SMS or instant messaging is that the message in TTY is transmitted in real-time i.e. it’s transmitted as you type. This is slightly faster than sending text messages.

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TTY was especially useful when landlines were common as messages could easily be sent over a landline voice call. Users would place the landline handset on top of a special device that looks like a typewriter. They would then type their message on the TTY device, which would encode the characters into audio tones, and then play those tones into the mic of the headset to transmit the signal. The receiving telephone would listen to the beeps and convert them into characters that would be visible on a corresponding TTY device.

TTY in modern smartphones

Today, most modern smartphones – including iPhones and Android devices – still support TTY mode. The feature is usually found under accessibility settings as it’s meant to be used by the hearing impaired.

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If you use the software TTY mode, the UI is very similar to that of a traditional SMS. You simply dial the number of the person you want to speak with while TTY mode is enabled, and then you can transmit text messages back and forth in real-time, faster than you would if you were sending an SMS or WhatsApp message.

These phones also support a hardware TTY mode where you can connect a TTY device to the phone.

Some modern TTY devices even do text to speech, where a text message sent over TTY reads the message out directly into a person’s hearing aid, and vice versa where it converts speech into a TTY-based text message. Modern smartphones can even keep a record of the transcripts, unlike the early TTY devices which simply interpreted the signals in real-time and kept no records.

Enable TTY on an iOS or Android device:

1. Open ‘Settings’

2. Navigate to ‘Accessibility’

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3. Tap ‘TTY’ or ‘RTT/TTY’ to enable the feature

4. You will now see an option to switch to TTY mode during a phone call. 

While TTY is a nifty accessibility feature that can be enabled on both an Android and iOS device, do bear in mind that your network provider needs to first support that mode for you to be able to use it. This service isn’t available in India at the moment, sadly, but given that instant messaging services like WhatsApp already enable real-time communication, and that many devices also support real-time text-to-speech conversion, this isn’t such a big deal in 2024.