For communication for people with hearing impairments. By use of the typewriter keyboard two people can type messages to each other over the telephone line. The conversation is showed on a small digital display. Some TTY models have a paper printout, direct connect and auto answer facility.
Modems There are many types of communication software that can be used with modems.
The National Relay Service can be used with most communications software when the settings are set to the correct values. This model effectively turns the TTY into a modem. Many television programs have subtitles transmitted with the picture. Some videos also contain subtitles or subtitles. Though an ordinary TV does not display them, there are TVs and VCRs with decoders that will put the subtitles at the bottom of the screen.