MacRumors forum members have been noticing the change. For example, user kre62 says:
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.
The change has been noticed by other users especially those with the iPhone 5 and an unlimited data plan; however, there has been positive responses from users with the iPhone 4S as well.
AT&T recently announced that it would expand FaceTime over Cellular at no extra charge for iOS 6 customers with an LTE device on any tiered data plan after intense criticism over its previous decision to make the feature only available to those on Mobile Share plans.