The TTY abbreviation stands for teletypewriter, a device that allows deaf or hearing-impaired individuals to communicate via the telephone by typing text messages. Cell phones with a TTY mode are compatible with this technology and perform the same service after they're connected to a TTY device.

TTY stands for “teletypewriter.” It was initially developed for people with hearing or speech difficulties to communicate over traditional telephone networks. TTY devices translate typed text into electronic signals sent across the telephone network and retranslated to text at the other end.