Sorry I am responding to everyone who has brought this issue up to make sure that the word gets out. I am glad to see that this is getting noticed. I went thru this today
AT&T wants to charge for it. Also caution: If you are "grandfathered" into an unlimited data plan and switch to a new "termed" data plan just to get face time available without wifi your unlimited data plan is no longer valid. Also note that AT&T no longer offers an unlimited data plan at this time so you cannot get it back
I downloaded IOS6 and turned my wifi off and tried facetime. It advised that I need to contact AT&T to make sure I had the applicable data plan.
I had an interesting conversation with AT&T today. They told me that I had to sign up for a new plan.
They fully admit that Facetime is interent based and goes over the internet when connected to wifi. I responded that when wifi is turned off, it goes thru the internet on the phone which is data. Since I have unlimited data they are now restricting my unlimited data. They won't deny that. They only state that AT&T offers a new plan which allows you to use facetime without wifi. I believe it was called "mobile sharing"
I escalated to three different supervisors until there wasn't a higher one present. They commited to have someone call me back tomorrow. I asked that take this as a formal complaint. I also advised that I would be contacting the BBB as they have stepped over the bounds of ethichal behavior.