A text telephone (TTY) is a device that allows individuals who are deaf, hard of hearing, or have speech disabilities to communicate over the phone using text. Users type their messages on a keyboard, and the text is transmitted over the phone line to another TTY user or a relay service. TTY devices typically have a small screen to display incoming messages. They can connect to standard telephone lines and are often used in conjunction with a relay operator, who reads the typed messages aloud to hearing individuals and types their responses back to the TTY user.