RTT stands for Real-Time Text, which is a feature that allows users to send text messages with a recipient during a phone call. It is an accessibility feature aimed at helping the deaf and hard-of-hearing community have real-time conversations over the phone. RTT works with TTY (teletypewriter) and doesnt require any additional accessories. During an RTT call, the text is transmitted instantly and in real-time as it is typed, usually without clicking the send button. RTT calls include an audio stream, and users can mute or un-mute their microphone. RTT calls use call minutes, just like a voice call. To use RTT, users need to turn on the feature in their phone app settings. Users can place a call with RTT, or they can switch from voice to RTT during a call. RTT calls are available for plans from carriers in the United States and Canada only.