TTY stands for "teletypewriter."
It is occasionally called a TDD, which stands for "Telecommunication
device for the Deaf."
Some government types tried to call it a TT (text telephone) for a while, but
it never caught on. (chuckle)
But here in the Deaf community, we call it a TTY.
For more information see the TTY
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars