For individuals who are deaf or hard of hearing, telephone communication involves communicating by text rather than by voice, typically using a teletypewriter (TTY), also known as a TDD (Telecommunications Device for the Deaf). A basic TTY consists of a keyboard, a display screen, and a modem, which operates over standard telephone lines. If a deaf individual is communicating with another TTY user, both users send and receive text. If a deaf individual is communicating with a hearing individual who doesn't have a TTY, they will use the Telecommunication Relay Service (TRS).
The TRS is a national service in which relay operators provide two-way translation between spoken word and typed text. The service was mandated by Title IV of the Americans with Disabilities Act of 1990 and is available free of charge. For more information about TRS, consult the Federal Communications Commission's Telecommunications Relay Services  page. The FCC also maintains a list of TRS by state and territory .
The Video Relay Service (VRS) is similar to the TRS, but a relay operator provides translation between spoken word and American Sign Language (ASL), rather than spoken word and text. The hearing user communicates by voice, the non-hearing user communicates by video using ASL, and the relay operator serves as a liaison, communicating by voice to the hearing party and by video using ASL to the non-hearing party. VRS is an important alternative to the original TRS, since many individuals with hearing impairments prefer ASL as their primary method of communication. VRS can occur over high-speed Internet connections with video conferencing software, such as Microsoft NetMeeting, or over special video-equipped phone terminals.
The Federal Video Relay Service  is available for federal employees and for the general public when accessing a Federal agency. For VRS needs outside of this scope, telecommunications providers in most states are now providing this service.
Another relay service, called the Speech-To-Speech (STS) relay service, provides communications assistants (CAs) for people with speech disabilities who have difficulty being understood on the phone. STS CAs are trained individuals familiar with many different speech patterns and skilled in language recognition. For a list of STS access numbers in the United States, consult the FCC Speech-To-Speech Relay Services  page.
-  Telecommunications Relay Services
-  TRS by state and territory
-  Federal Video Relay Service
-  Speech-To-Speech Relay Services