AT&T won’t charge for FaceTime over cellular — but there’s a catch

Apple’s(s aapl) iOS 6 software update for iPhones is coming soon and will, for the first time, enable its FaceTime video chat service to operate over a cellular connection, instead of just Wi-Fi. Sprint(s S) has said it won’t charge for Apple video calls over its cell network, while Verizon(s VZ) hasn’t given an answer either way. On Friday, AT&T(s T) said it will not charge for FaceTime over cellular either, provided a customer has signed up for one of its new Mobile Share plans.

AT&T told MacRumors:

AT&T will offer FaceTime over Cellular as an added benefit of our new Mobile Share data plans, which were created to meet customers’ growing data needs at a great value. With Mobile Share, the more data you use, the more you save. FaceTime will continue to be available over Wi-Fi for all our customers.

It sounds like, by adding that FaceTime “will continue to be available over Wi-Fi for all customers,” that AT&T won’t simply charge extra for the privilege of using it if you don’t have one of these plans, but that you can’t use it all over cellular; Wi-Fi is the only other option.

AT&T introduced its new shared wireless plans in July and they go into effect Aug. 23. The plans charge a per-line rate for each device, and combine unlimited voice minutes and texts with a flat fee for data, which is shared by each device on the plan.

They’re a little bit cheaper, and optional for new or current customers. So it looks like the carrier is using FaceTime over cellular as a bit of a carrot to encourage heavy users of the video service to convert or sign up for the new plans.