AT&T may be on the brink of achieving the improbable. The mobile carrier is reportedly considering charging subscribers extra to use Apple's FaceTime video chat app on their mobile phones. Were they to actually do so, they'd likely be in violation of the FCC's net neutrality rules for mobile broadband -- a remarkable feat, given how wildly permissive those rules are.

With regard to net neutrality, the FCC divides broadband into two categories: fixed and mobile. The rules for fixed broadband are meant to prevent internet providers from blocking or favoring certain types of traffic on their networks, but ISPs are already exploiting loopholes in the regulations to favor their own content. But when it came to mobile broadband, the FCC took a more laissez-faire approach, arguing that it needs to “better understand how the mobile broadband market is developing before determining whether adjustments to this framework are necessary.”

However, one thing the FCC did prohibit is the blocking of video chat and voice-over-IP apps that compete with mobile carriers' telephone service:

A person engaged in the provision of mobile broadband Internet access service, insofar as such person is so engaged, shall not block consumers from accessing lawful websites, subject to reasonable network management; nor shall such person block applications that compete with the provider's voice or video telephony services, subject to reasonable network management.

According to TechCrunch, AT&T CEO Randall Stephenson isn't denying rumors -- first reported by the Apple-watchers at 9toMac -- that they're considering charging to use FaceTime, saying only that “it's too early to talk about pricing.” Preventing subscribers from using Apple's FaceTime (unless they pay AT&T) would certainly seem to run counter to the net neutrality rules, and consumer advocacy groups like Public Knowledge are letting AT&T know as much. “If AT&T intends to charge users an extra fee to use FaceTime over cellular networks, this would be a clear violation of the FCC's open Internet rules,” says PK's Harold Feld.

So why would AT&T stumble into one of the vanishingly few violations of the net neutrality rule? The allure of the double-dip.

There is nothing mobile carriers would love more than the freedom to charge twice for the same data. When you sign up with AT&T, you're allotted a fixed amount of data per month. Even if you don't use it, you've already paid for it. If AT&T starts charging to use FaceTime, it will have succeeded in getting you to pay to use the data you've already paid for. The flip side to this scheme is AT&T's other scheme -- verified to be in the works -- to charge app developers for the data their subscribers use, thus charging content providers for access to consumers and vice-versa. That's a more promising avenue for AT&T, as there doesn't seem to be anything in the net neutrality rules to prevent it.

And it would screw over consumers, as would the rumored FaceTime double-dip, which seems increasingly to be the point.