A Telecommunications Display Device (TDD), also known as a text telephone, is a telephone equipped with a keyboard and a display for people who are hearing- or speech-impaired. A TDD allows individuals to send and receive typed messages using its keyboard. Both home and public telephones can be equipped with a TDD. Public TDD pay phones have a keyboard drawer that slides out only after a call has been placed to and answered from another TDD phone so that the keyboard is protected from vandalism or other damage.
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