This video showcases the new pop-up dialogue box that interrupts you when trying to enable FaceTime over cellular in iOS 6 beta 3.
Apparently, AT&T has a scheme in the works to pry more dollars from their iPhone customers. As Cody noted via Twitter, perhaps they're thinking about rebounding after taking a hit on text messaging fees due to iMessage.
Take a look inside as we demonstrate the differences between an AT&T iPhone 4S, and a Verizon iPad 3, when attempting to enable FaceTime over cellular...