A teletypewriter (TTY) is a data terminal that people who are hearing impaired or speech impaired can use to transmit and receive text through a telephone system. A TTY is also referred to as Telecommunications Device for the Deaf, or TDD. A typical TTY resembles the keyboard of a laptop computer with a one-line or a two-line alphanumeric display. The TTY is silent when it is not used to transmit text. As a user types on the device, the TTY emits audio tones that the telephone network transmits.
Not all TTY users transmit and receive messages with TTY devices. Approximately half of the people who rely on TTY devices are hearing impaired, but can speak clearly. They often prefer to receive messages on their TTY devices and then speak in response. This process is referred to as Voice Carry Over, or VCO.
Messaging only supports the Audix TUI with the TTY devices. Also, Messaging does not provide automatic TTY support in Messaging mailboxes. Administrators need to enable TTY support. In Messaging, administrators can configure mailboxes so that callers can select TTY-format, or voice prompting from the same mailbox.