Telecommunications Relay Services (TRS) were created to allow people who have difficulty hearing or speaking on the telephone to communicate with voice telephone users. Under Title IV of the Americans with Disabilities Act (ADA)  , each state, the District of Columbia, Puerto Rico, and all of the U.S. territories must provide free relay services.
TRS uses "communications assistants" to facilitate the telephone calls, local and long distance, at no cost to the user, 24 hours a day, 7 days a week. There are no restrictions imposed on callers concerning the length, frequency, or nature of their calls. A person who is deaf or heard of hearing or has a speech disability, or a person without such a disability, can initiate a call by dialing 7-1-1 to connect to a relay service anywhere in the United States.
The following are the types of telephone relay services available as of October 2007; as technology advances, newer forms of TRS may become available. The descriptions assume that the caller is a person who is deaf or hard of hearing, or has a speech disability, although a person without a disability may initiate a call.
Text-to-Voice TTY-based (traditional) TRS: In this type of relay service, the caller and the communication assistant have text telephone devices with a keyboard, but the called person does not. The communication assistant reads what the caller has typed to the called person and then types and sends the called person's responses back to the caller using the text telephone.
Video Relay Service (VRS): Persons whose primary language is American Sign Language (ASL) can use this Internet-based form of TRS via the use of video conferencing equipment. Instead of typing text, the deaf person signs to a certified interpreter who performs the functions of a communication assistant. The interpreter speaks what is signed to the called party, and signs back the response back to the caller.
Internet Protocol (IP) Relay: IP Relay is similar to TTY-based TRS except that it uses the Internet (via a computer, PDA or other web-enabled device) rather than the traditional telephone network for the communication between the deaf or hard of hearing person or speech disabled person and the communication assistant.
Captioned Telephone Service: Captioned telephone service, like VCO, is used by persons who are deaf or hard of hearing, but have some residual hearing. It uses a special telephone that has a text screen to display captions. A captioned telephone allows the caller, on one line, to speak to the called party and to simultaneously listen to the other party while reading captions in the display. A two-line captioned telephone service is also available where the communication assistant, instead of typing the response as in traditional TRS, repeats or re-voices what the called party says, while speech recognition technology automatically transcribes the communication assistant’s voice into text, which is then displayed on the captioned telephone.
Internet Protocol (IP) Captioned Telephone Service: IP captioned telephone service combines captioned telephone service with IP Relay, and uses the Internet to connect the deaf or hard of hearing caller with the communication assistant. The user may utilize a computer, PDA or other web-based device to simultaneously listen to and read the text of what the called person is saying.
Voice Carryover(VCO): In this form of relay service available in both traditional TRS and VRS, the caller can speak but is unable to hear. The caller speaks to the called person and the communication assistant types or signs the called person's replies to the caller.
Hearing Carryover(HCO): In this type of relay service, the caller can hear but has difficulty speaking. The communication assistant reads the caller's text to the called party. The caller then listens to the called party's responses.
Speech-to-Speech(STS): In this type of relay service, no special telephone devices are required. Speech-to-speech relay services use communication assistants who have been specially trained to understand a variety of speech disorders. The caller speaks, and the communication assistant repeats what the caller has said in a clear and understandable voice to the called person. The caller then listens to the called party's responses.
Shared Non-English Relay Services: The FCC requires interstate (between states) TRS providers to offer Spanish-to-Spanish services between a hearing or speech disabled Spanish language user to a non-disabled Spanish language user. Both the caller and the called person must be using Spanish, hence the term “Shared Non-English Relay Services”. Although not required, many states with a large population of Spanish language users offer intrastate (within the state) Spanish relay services. TRS providers may also voluntarily provide other shared non-English language services, such as French-to-French, on an interstate basis and be compensated from the federal TRS fund. This service is also available through VRS.
For more information on TRS consult the Federal Communications Commission's Consumer Fact Sheet Telecommunications Relay Services .
-  Title IV of the Americans with Disabilities Act (ADA)
-  Telecommunications Relay Services