Relay
One of the most common uses for a TTY is to place calls to a Telecommunications Relay Service (TRS), which makes it possible for the Deaf to successfully make phone calls to regular phone users.
The voice recognition systems are in limited use, due to problems with the technology. A new development called the captioned telephone now uses voice recognition to assist the human operators. Newer text-based communication methods, such as short message service (SMS), Internet Relay Chat (IRC), and instant messaging have also been adopted by the Deaf as an alternative or adjunct to TTY.
Read more about this topic: Telecommunications Device For The Deaf