Having come under fire with the announcement that only customers signed up to one of its Mobile Share plans can utilise Apple’s FaceTime service over a cellular connection, US operator AT&T has taken the legal approach to explain its decision to customers, stating that because the app is preloaded, it can effectively limit its use.

Some customers have argued that AT&T’s limitation on FaceTime use could infringe net neutrality rules and may warrant an FCC investigation. The carrier’s response? You’re all wrong.

AT&T goes to the effort of detailing the requirements it must meet so that it doesn’t infringe net neutrality requirements, one that will mean it remains fully transparent to consumers and that it will not block apps that compete with its own voice or telephony services.

AT&T’s SVP of regulatory affairs Bob Quinn then argues that the rules do not take into account pre-installed apps:

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.

As The Verge points out, would things have been different if Apple made FaceTime available as a standalone download? Does this mean further restrictions on Google’s Android and Microsoft’s Windows Phone platforms?

Quinn says AT&T customers can still use it over Wi-Fi (gee, thanks) but drops another key reason as to why it is limiting access to Mobile Share plans: bandwidth.

He notes: “We are broadening our customers’ ability to use the preloaded version of FaceTime but limiting it in this manner to our newly developed AT&T Mobile Share data plans out of an overriding concern for the impact this expansion may have on our network and the overall customer experience.”

Considering AT&T had already imposed data caps on the majority of plans, which are designed to reduce strain on its networks and improve service for all, the argument is a weak one.

AT&T believes it will escape investigation from the FCC, but today’s comments will almost certainly rile its customers even more, further increasing the changes of the regulator getting involved.