Telecommunications Relay Service (TRS, Relay Service, IP-Relay) is an operator service used by deaf persons and those with other hearing difficulties , to allow them to place telephone calls.

In the most common use of TRS, typed messages are relayed as voice messages by a TRS operator, and vice-versa. This allows callers unable to use a regular telephone, to be able to place telephone calls to people who use a regular telephone, and vice-versa.

In less common uses of TRS, there is Voice-Carry-Over (VCO), Hearing-Carry-Over (HCO). VCO allows the TRS to use voice for outgoing communications and text for incoming communications. HCO is the opposite of VCO. The HCO method is most commonly used by people who have difficulty speaking, but have no difficulty hearing voice.

Most TRS operators use regular keyboards to transcribe spoken voice as text for relaying. However, some TRS services may use stenotype or stenomask equipment, similar to those used by court reporters and closed captioning systems.

Calls to a TRS are usually made by TDD (telecommunications devices for the deaf) unit, via computer modem, or via Internet. Recently, there have been SMS/AIM based relay services provided by deaf-oriented wireless services. A new method for the deaf to make phone calls is called a captioned telephone, which uses voice recognition.

Major telephone-line-based relay services

• Phone number 711 in all of North America. This service is similar to dialing 411, 611 or 911, and is dialed via a TDD, a computer modem or a regular telephone.
• Phone prefix 18001, followed by the destination number, for TDD to regular telephone or 18002 for regular telephone to TDD in the UK. For more details of this service see Typetalk.

Major Online Relay Services

• Sprint Relay Online
• MCI IP Relay
• AT&T Relay Call
• Hamilton IP Relay