What Is the Difference Between TTY and TDD?

By Diana O'gilvie

Technology has made leaps and bounds in providing communication options for the disabled. TTY and TDD enable hearing-impaired and speech-impaired individuals to communicate over the telephone. TTY and TDD work in conjunction--there is no distinguishing difference.

What is TDD?

TDD, or Telecommunications Device for the Deaf, is a software program that enables deaf or mute individuals to communicate over the telephone with TTY devices.

What is TTY?

TTY--or telephone typewriter, teletypewriter or text phone--is a device used by deaf or mute individuals to communicate over telephone lines. The device is a "QWERTY" keyboard that is similar to a computer's but smaller. A screen attached to device shows words as they are being typed.


The TTY is connected to a phone line. The Direct Connect ensures that the phone cord is plugged directly into the phone jack. A flashing light alerts when there is an incoming call.

Technological Advances

TTY/TDD is available as a portable device and is used in place of a land line. Some TTY/TDD devices can be attached to hearing aids.


Callers must take turns when sending messages. You cannot interrupt as in a normal conversation. To facilitate proper protocol, codes are used at the end of each transmission to let the other person know when it's his turn.