|In spite of earlier statements by the carrier, AT&T appears to be extending cellular FaceTime to all compatible devices on its network, note forum posters at MacRumors. It had been announced that while cellular FaceTime would no longer be restricted to Mobile Share plans, the option would still require a tiered data plan and a device with LTE. By definition that would block the iPhone 4S and/or anyone on a grandfathered unlimited plan; anything earlier than the 4S is unsupported because of Apple's own restrictions in iOS 6.
Some of the forum posters say, though, that they have been able to turn on FaceTime both on the 4S and on iPhone 5s using unlimited data. Not everyone has had success, but that could simply mean that AT&T is still rolling out the feature. AT&T itself originally stated that its FaceTime support could take eight to 10 weeks to deploy. In any case, people who have had the option turn on have sometimes had to restart their phones first.
At this stage it remains uncertain if the wider FaceTime access is a mistake on AT&T's part or intentional. The carrier was widely criticized when FaceTime was limited to Mobile Share, and backed off mainly to avoid government scrutiny. It also faces sharp competition from Verizon and Sprint, though, since neither of which have any artificial limits on FaceTime calls.