A Text Telephone, also known as a TTY (Teletypewriter), is a device that allows individuals who are deaf, hard of hearing, or speech-impaired to communicate over the telephone. It uses a keyboard for typing messages and a display screen or printer to read incoming messages. Users can send and receive text messages in real-time, making phone conversations accessible. The TTY connects to a standard telephone line and can also be used with relay services. In a relay call, a communication assistant reads the typed message to the hearing party and types their spoken response back to the TTY user, facilitating effective communication.