AT&T has responded to concerns about their new FaceTime Over Cellular policies which will require their customers to be on a mobile share plan in order to utilize the feature. While many believe this restriction violates the FCC's net neutrality laws, AT&T doesn't think it does.
While the FCC does restrict companies from blocking apps, AT&T says that only applies to downloadable apps and not pre-installed apps. Since FaceTime comes pre-installed on every iOS device, they have the right to restrict use.
The FCC’s net neutrality rules do not regulate the availability to customers of applications that are preloaded on phones. Indeed, the rules do not require that providers make available any preloaded apps. Rather, they address whether customers are able to download apps that compete with our voice or video telephony services. AT&T does not restrict customers from downloading any such lawful applications, and there are several video chat apps available in the various app stores serving particular operating systems. (I won’t name any of them for fear that I will be accused by these same groups of discriminating in favor of those apps. But just go to your app store on your device and type “video chat.”) Therefore, there is no net neutrality violation.
Whether or not the FCC will agree with AT&T isn't yet clear. The New York Times recently stated that AT&T actually is in violation of FCC regulations and that the carrier can not block applications that compete with a carrier's own voice or telephony services.
Regardless whether the app is pre-installed or not, FaceTime should probably be considered a competing service. The fact that a specific data plan is required in order to use it is another contention point. Data is data and regardless what tier you're on, you're paying for the same bits and bytes. It still begs the question, why should one tiered data plan be treated different than any other? If customers go over their allotment, charge them appropriate overages and call it a day. Forcing customers on a plan they don't want or need doesn't seem to be in anyone's best interest.