FaceTime over AT&T's 4G (you know, 3G) on my iPhone 4s (with a 2GB data plan) was enabled as of a few days ago. Haven't checked the settings since then, but I just updated to iOS 6.1 from 6.0.1, and after a message came up about saying that the iPhone was now using the new iCloud email address for iMessages, I decided to check on FaceTime, and it appears that the cellular data option for FaceTime is switched off again (and I can't enable it, just shows the 'call AT&T' popup). I don't really know for sure if I can blame iOS 6.1 because as its been a few days since I checked the setting it could be coincidence.
What do you think? A glitch in AT&T's system that accidentally temporarily enabled my 4G FaceTime? Something about the update turning it off? When I asked AT&T, they were surprised that it was even working at all a few days ago.
Best Answer
It isn't exactly iOS 6.1 and it sounds like AT&T at it again. I updated my iPhone 4S to iOS 6.1 yesterday as well and my Facetime over Cellular is still enabled. I am on a shared data plan, though, which has always - since iOS 6.0 - had the option to Facetime over Cellular.
I think AT&T's response when you asked them shows who is ultimately at fault here. Even though 6.1 isn't exactly at fault, it is possible that AT&T hasn't fully opened the possibility to Facetime over cellular to users with data packages like yours, and that upgrading to iOS 6 somehow re-instated that until AT&T does better opening it up.