A TTY (teletypewriter) is a communication device used by people who are deaf, hard-of-hearing, or have severe speech impairment.
♦ It is also sometimes called a TDD, or 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 messages back and forth to one another instead of talking and listening.
A TTY is required at both ends of the conversation in order to communicate.
♦ People who don't have a TTY can communicate with a TTY user through Telecommunications Relay Service (TRS).
A special operator types whatever you say so that the person you are calling can read your words on his or her TTY display.
TRS providers – generally telephone companies – are compensated for the costs of providing TRS from either a state or a federal fund.
There is no cost to the TRS user.