The FCC this week granted AT&T a limited waiver to implement Wi-Fi calling even though it does not support text telephony (TTY) for deaf and hard-of-hearing customers.

For decades, the agency has required telecom and companies that provide communication services to support TTY, which lets people communicate via text. TTY, however, doesn't really play nice with IP-based services like Wi-Fi calling, so companies like AT&T are experimenting with real-time text (RTT), which provides communication in real-time and works over the Web.

The FCC's waiver lets AT&T move ahead with Wi-Fi calling without implementing TTY until December 2017.

In making its decision, the agency said it understands "that there are major technical barriers to reliably supporting TTY transmissions over IP networks." TTY is also "seldom used on wireless networks [and] a significant percentage of former TTY users have abandoned their TTYs over the past several years" (156,000 minutes in August 2015 vs. 787,511 minutes in August 2008).

The move also does not affect wireline IP-based services or non-IP-based wireless services, so consumers who rely on TTYs for access via their home and business connections will not lose service, the FCC said.

"We're grateful the FCC has granted AT&T's waiver request so we can begin providing Wi-Fi calling," Jim Cicconi, AT&T senior executive vice president of external and legislative affairs, said in a statement.

The carrier did not indicate when it would start providing Wi-Fi calling. It was actually available to AT&T customers using the iOS 9 beta, but disappeared with the full rollout, ostensibly because of the waiver issue.

The FCC, however, hasn't exactly been very strict when it comes to this issue. T-Mobile and Sprint, for example, have already rolled out Wi-Fi calling without obtaining an FCC waiver, and AT&T used its statement today to criticize its rivals.

"We are left scratching our heads as to why the FCC still seems intent on excusing the behavior of T-Mobile and Sprint, who have been offering these services without a waiver for quite some time," Cicconi said. "Instead of initiating enforcement action against them, or at least opening an investigation, the agency has effectively invited them to now apply for similar waivers and implied that their prior flaunting of FCC rules will be ignored."

In its ruling, the FCC said only that "given the limitations of TTY technology in a wireless IP network as enumerated in the record of this proceeding, the extent to which such providers are in compliance with our TTY obligations remains unclear." It would "not be appropriate" to grant other providers a waiver without more information, the FCC said.

"T-Mobile is in full compliance with the FCC rules and supports TTY," a company spokesman told PCMag. "We have no knowledge of the network configuration or planned service offerings that drove AT&T to seek the requested waiver."

Sprint declined to comment.