AT&T has offered a video conversation service, called VideoShare.  As best I can tell, they shut it down about a year ago.  But the FCC could easily conclude from that example that FaceTime should be considered competitive to AT&T's actual or potential services.

The broader issue is app discrimination of any kind that could benefit AT&T.  If they force users into newer, more profitable plans or even just suppress usage to keep costs down, AT&T benefits.  This is only one step away from more obvious self-interested discrimination, such as pay-to-play (preferential performance for apps/services that pay AT&T a cut).  We know carriers would love to go there.

I think there is a very strong common-sense argument that service limitations should be application-agnostic (e.g. aggregate data rate limiting or usage caps).  This will be a good test of whether the current rules + public pressure are sufficient to protect app-agnosticism (note I stay away from the term "net neutrality" because it implies different things to different people).  If not, i.e. if AT&T keeps blocking FaceTime for some users, I would expect a new groundswell of support for strengthening the rules. 

Carriers have deployed caps and/or overage to monetize traffic load. If they start throttling/blocking on a per app basis then a user-experience is further muddied. Allowing certain apps on specific plans just confuses the hell out of consumers. If facetime were to become popular my guess is that consumers will go for a simple plan.

Yeah, but you could argue that video calls compete with regular calls and texts. It's also interesting that you can use other video chat services on AT&T's network, so it's singling out FaceTime. I get why it's doing it - to limit the traffic it wil cause and encourage people to move to mobile share plans - but we'll see what the FCC says.

Does AT&T even offer a video conversation service? It may be difficult to win a claim that Facetime competes with AT&T's voice service when the two are qualitatively different.