How Hearing Impaired Telephones Work

If you don’t have a TTY unit or TDD, you can use a telephone relay service to communicate by phone with someone who is deaf or hard of hearing. Telephone relay services are required by the Americans with Disabilities Act, with services in English and Spanish, and regulated by the FCC. And while this variation on hearing-impaired telephones started as something like a translation service, variations like IP relay make more use of electronic technology.

The national Telecommunications Relay Service (TRS) is free and available 24 hours a day, seven days a week, to handle voice-to-TTY and TTY-to-voice calls. Various relay providers offer services in each state.

Here’s how the TRS works. The person placing the call accesses TRS from any TTY or standard phone by calling 7-1-1. The caller is connected to a communications assistant who relays communication between the caller and the recipient. A hearing caller, for example, speaks the message to the assistant, who types and relays it to the deaf recipient, who reads it on his TTY display screen. The recipient responds with a typed message, which the assistant reads to the hearing caller [sources: Occupational Safety and Health Administration and Gallaudet University].

The TRS can handle calls from computers via IP relay, as well as from TTYs. IP relay allows users to communicate using a computer and modem rather than a TTY unit. The IP relay starts with the caller’s computer or mobile device and goes to the IP relay center, which usually is accessed from a Web page.

There the call goes to a communication assistant, who sends the message on through the switched telephone system, converting it to either text or spoken word, depending on whether the recipient can hear. There is no extra charge for IP relay calls.

IP relay offers the advantage of being available through any device with Internet access. Also, transmission may be faster, and users can make multiple calls, have conference calls or browse the Web while on a call [source: FCC].

The newest addition is video relay service. It goes a step further by adding visuals to the conversation. This requires a high-speed Internet connection. Once that's established, a sign language interpreter reads the signed communication from the hard-of-hearing caller and speaks the message to the hearing recipient on the phone.

Gallaudet University provides information about both IP and video relay services.

For lots more information about hearing impaired telephones and related topics, check out the links below.

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