In one of Apple's written responses to the government (I can't remember if it was after the "locationgate" or "privacygate" issue), Apple clearly stated their agreement with AT&T requires that AT&T approve Apple providing voice over IP features utilizing the cell network, which includes FaceTime over 3G.
In order to finally get FaceTime over 3G approved by AT&T, it would appear that Apple had to provide AT&T with a mechanism to enforce specific data plans for customers wishing to use FaceTime over 3G, i.e. no unlimited data plan.
Well that would explain it quite clearly then. Must have been something that stemmed from their original agreement? I'm sure they haven't been doing the same with hundreds of other carriers worldwide.
Don't forget that thanks to iMessage, AT&T has lost bucket loads of cash from their ripoff SMS text cash cow. AT&T wants to get some of that money back.
-ITG
I've heard this a lot. Has AT&T really been charging insane prices for SMS? Most carriers in Canada (and I'd assume other countries are even better) either include unlimited sms/mms or charge $5 for unlimited use of it.