TTY stands for "teletypewriter," which is a device initially created to allow individuals with hearing or speech impairments to communicate by sending typed text over standard telephone lines. In modern smartphones, TTY mode replicates this functionality, enabling text-based communication during a voice call. TTY mode includes several settings, such as TTY Full, TTY HCO (Hearing Carry Over), and TTY VCO (Voice Carry Over) .
Depending on the phone, it may have a built-in TTY software, allow you to connect the phone to an external TTY device, or both. TTY Full mode allows both the sender and receiver to communicate through TTY messages. TTY VCO mode is for hearing-impaired users who can send messages through voice but need to receive messages on a TTY text display. TTY HCO mode is for users who can receive voice messages but need to send text messages.
TTY mode is a legacy technology, and many hearing or speech-impaired people can utilize SMS to communicate. There are also real-time IP technologies to make communication more accessible, but these require either a data plan or a digital telephone line.
