T-Mobile US Inc. and Sprint Corp. (NYSE: S) have both been offering VoWiFi for years. AT&T Inc. (NYSE: T) was in no rush to also provide the feature, but once it decided to do so, the FCC rule requiring Teletype (TTY) got in the way.
AT&T has been openly irritated that T-Mobile and Sprint are both offering VoWiFi in apparent contravention of the TTY rule, but opted to go the official route. It developed an alternative to TTY called Real-Time Text (RTT) that, unlike TTY, works well on IP networks, and then finally only last week filed a request from the FCC for a waiver from the TTY rule. (See AT&T Asks FCC to Grant WiFi Calling Waiver .)
The FCC granted a waiver to AT&T that will last until 2017 or until the Commission makes a final determination on whether or not to continue requiring support of TTY, whichever comes first (the FCC's intention is to wrap up the issue by no later than 2017).
The FCC also invited other companies to file for a waiver similar to the one it just granted AT&T.
TTY works only fitfully on IP networks, the FCC notes in its waiver, and yet many people still use it. The FCC will no doubt consider replacing the requirement for TTY with a requirement for RTT or some similar technology to better accommodate hearing-impaired customers.
— Brian Santo, Senior Editor, Components, T&M, Light Reading