Good news for AT&T customers with iDevices -- the carrier appears to be extending FaceTime over cellular to all iPhone customers.
AT&T announced earlier this month that it would enable FaceTime over cellular for customers "with an LTE device" on a "tiered data plan" using iOS 6. This caused a bit of a stir because it excluded both grandfathered customers with unlimited data plans, and those with the iPhones 4S handsets.
MacRumors' forum users report that the feature has been quietly enabled. Forum user "kre62" appears to have been the first to notice the change [sic]:
In a recent thread we were discussing AT&T members getting facetime with LTE devices and tiered plans. However I noticed today that I have facetime over cellular and I have an unlimited plan on my 5.
I just turned off my other phone, a 4S and turned it back on, only to find the switch flipped to ON for facetime over cellular. Both phones work perfectly over cellular.
I also checked a few coworkers phones, all now have FT over cellular.
If you have ATT, turn your phone off and back on and report back if you now have FT over cellular.
Several other forum users have conformed "kre62's" findings, while others claim that it they can't enable the feature. (iOS 6 only supports FaceTime over cellular on the iPhone 4S, iPhone 5, and iPad 3 or higher.)
I've reached out to AT&T for comment on this possible change in policy, and will update this post when I hear anything.