If you attempt to activate FaceTime over cellular in the iOS 6 settings, you'll be presented with a dialog that gives you the option to either call AT&T to activate the service, or go to its website to do so there, instead.
It's the same basic dialog that appears when AT&T subscribers attempt to enable data tethering on their iOS devices, another feature of iOS that AT&T monetizes. Of course, as iOS 6 hasn't been released yet, this dialog blocks the ability to activate FaceTime over cellular.
When questioned about it, AT&T said,
"We’re working closely with Apple on the new developer build of iOS6 and we’ll share more information with our customers as it becomes available."
In other words, no comment.
Anyone who has used a third-generation ("new") iPad on Verizon knows that it does not charge extra for data tethering on that device (although data use is, of course, charged against your data plan). AT&T, on the other hand, does charge extra.
With that, it doesn't seem like either carrier has "changed its mind" with regard to these "extras" embedded in iOS.
Depending on how much AT&T charges for the feature, there may not be much uptake. After all, nowadays folks have access to wi-fi much, if not most of the time. Would you pay for something you won't use that often?