{mosads}Consumer advocacy groups Public Knowledge and Free Press argued that the restriction violated the FCC’s net-neutrality rules, which prohibit mobile service providers from blocking applications that compete with their own voice services.

FCC Chairman Julius Genachowski had declined to say whether he thought AT&T’s FaceTime restriction was illegal, but he said he would review the complaints and act if the commission found a violation of its rules.

In a blog post on Thursday, AT&T Senior Vice President Jim Cicconi said that because the company has so many iPhone customers, it needed to act cautiously to prevent congestion on its network. Streaming video uses up more bandwidth than do phone calls.

He said there was no way for the company’s engineers to “effectively model usage, and thus to assess network impact.”

“It is for this reason that we took a more cautious approach toward the app. To do otherwise might have risked an adverse impact on the services our customers expect — voice quality in particular — if usage of FaceTime exceeded expectation,” he wrote.

He said that within eight to 10 weeks, FaceTime will be available on AT&T’s network to customers on tiered pricing plans if they have an LTE device, such as the iPhone 5. 

“We will continue to gather and assess the network data on this issue over the next few months and anticipate that we will be able to expand the availability of FaceTime to our customers on other billing plans in the near future,” he wrote.

Consumer advocacy groups had complained that AT&T’s restriction was a particular hardship for deaf and hard-of-hearing customers, who rely on FaceTime to communicate.

Cicconi said AT&T will offer new billing plans specifically for deaf customers.

Free Press and Public Knowledge said they will file a formal complaint with the FCC if AT&T fails to lift the restriction in a timely manner.

“Our primary goal all along has been to bring a swift end to AT&T’s practices that harm consumers, competition and innovation,” Public Knowledge senior staff attorney John Bergmayer said. He added that the groups are willing to wait and see if AT&T follows through with its commitment but that they are prepared to take legal action.

“The law is clear,” Free Press policy director Matt Wood said. “AT&T cannot block FaceTime based on claims of potential congestion. There’s nothing even remotely reasonable about that approach.”

Rep. Anna Eshoo (D-Calif.), a vocal supporter of the FCC’s net-neutrality rules, applauded AT&T’s announcement.

“This is a victory for consumers and for those who know a free and open Internet is vital to sustaining our rapidly expanding mobile technology market,” she said.

—Updated at 6:26 p.m.