While I am not sure what the exact acronym wording stands for, I can tell you it is a method for allowing deaf people to communicate by translating voice commands into text type messages, and vice-versa. Both sender and recipient must have TTY mode set. Someone who has a little bit more knowledge on this can correct me if I am wrong. JohnEB
Text Telephone / Teletype Terminal / TeleTYpewriter
Telecommunication Device for the Deaf
A TTY is a special device that lets people who are deaf, hard of hearing, or speech-impaired use the telephone to communicate, by allowing them to type text messages. A TTY is required at both ends of the conversation in order to communicate.
It can be used with both land lines and cell phones. Unlike text messaging, it is designed for synchronous conversation, like a text version of a phone call.
A modern digital cell phone must support a special digital TTY mode in order to be compatible with a TTY device.
tty is not actually an acronym it stands for Teletypewriter machines which took the place of Telegraph Keys.
TTY machines have been adapted for deaf people who call in to a TTY operator who calls the destination and provides the voice link. the tty operator and the deaf person communicate via the TTy link and the TTya operator relays the message back and forth.
PCs using Modems used to have TTY capability where the deaf guy could use a pc to dial up the TTY operator just like he had a teletypewriter machine.