In phone calls, TTY stands for teletypewriter, a device or functionality that allows users to communicate via typed text rather than speech.

TTY stands for TeleTYpewriter. It allows for people who are hard of hearing or deaf to receive and send text messages over phone lines. It works by converting tones to text that the receiver can understand. The sent text is then converted to tones and back again into a text.

TTY (short for teletypewriter), also known as telecommunication device for the deaf (TDD) or text telephone, is a term used for devices that are meant for sending texts over phone lines. It allows text messages to be sent and received synchronously.