An RTT call refers to a real-time text call, which is a feature that allows users to send text messages in real-time during a phone call. This feature is particularly useful for people who are deaf, hard of hearing, deaf-blind, or have speech-related disabilities. During an RTT call, the text is transmitted instantly and in real-time as it is typed, usually without clicking the send button. Both parties can type letters that immediately appear on the other side, though common courtesy dictates that you should let the other side finish their sentence to avoid interrupting them. RTT calls include an audio stream, but you can mute or unmute your microphone. To use RTT, you need a wireless handset like an iPhone or Android phone using IP-based technology on networks that support RTT. To make an RTT call, you need to enable the feature in your phone settings.