AT&T’s statement to Engadget, translated by me:
All AT&T Mobility customers can use any video chat app over cellular that is not pre-loaded on their device, but which they download from the Internet.
Remember that whole kerfuffle over how FaceTime was disabled over cellular unless you bought a much more expensive plan? We liked that PR disaster so much that we’d like to repeat it.
For video chat apps that come pre-loaded on devices, we offer all OS and device makers the ability for those apps to work over cellular for our customers who are on Mobile Share, Tiered and soon Unlimited plan customers who have LTE devices.
Don’t blame us, man. Blame Google. They’re the ones who have the most skin in the game if Hangouts are available over our cellular network.
It’s up to each OS and device makers to enable their systems to allow pre-loaded video chat apps to work over cellular for our customers on those plans.
Seriously — ask Google. File one of those bug reports or something and I’m sure they’ll get back to hey where are you going come back here.