Basically, AT&T sees them in the right to limit FT to shared data plans, even though iPhone users demand a more “open” policy on the usage of their data.
It’s actually a pretty complex situation: a user sees their data as their own, wanting some empowerment over what they choose to do with their allotment. AT&T wants to control the experience of data usage by limiting FT usage over 3G, as it will provide an overall improvement to the network by making it so that FaceTime only works on a small portion of customers’ data plans. Sometimes what people want isn’t the best option, at least according to AT&T.
The last paragraph points to this compromise:
We will be monitoring the impact the upgrade to this popular preloaded app has on our mobile broadband network, and customers, too, will be in a learning mode as to exactly how much data FaceTime consumes on those usage-based plans. We always strive to provide our customers with the services they desire and will incorporate our learnings from the roll-out of FaceTime on our mobile broadband network into our future service offerings.
Allowing FaceTime on cellular data through shared plans is an experiment. This could lead to opening the floodgates to all plans in the future, or it could lead to an even more limited use of FT on cellular data plans. The fact is that Apple has actually made video calling prevalent, so AT&T needs to brace for a future filled with this communication.