Over at AT&T, FaceTime on a cellular connection will be available only to those customers who sign up for the carrier’s new Mobile Share data plans. 

Users who stick with their existing plans will only be able to use the Apple video calling application over a Wi-Fi connection.

When Apple unveiled iOS 6 back in June, the company said the new iteration of its mobile operating system would allow FaceTime to run over a cellular connection. 

AT&T is calling FaceTime on cellular an "added benefit" of its new Mobile Share data plans.  

"With Mobile Share, the more data you use, the more you save," the company said in a statement, noting that FaceTime will continue to be available over Wi-Fi for all our customers. 

AT&T has long allowed various over-the-top services, such as Tango, to place video calls over a cellular connection. AT&T has not said whether it will limit those services as well. 

AT&T unveiled its new Mobile Share plans back in July and they will go live on Thursday. The carrier has built savings into the new plans that give discounts to customers for using more data. The larger the data bucket, the less the customer pays per gigabyte, with an additional reduction of the per-monthly fee for each smartphone added to the shared plan. 

For instance, a 1 GB bucket of shared data costs $40 per month, while the connection fees for each additional smartphone on that plan run $45 per month. However, the monthly smartphone connection fee is just $30 per month on a 15 GB shared bucket of data costing $150. Connections for additional devices to plan include $30 for a feature phone or quick-messaging device; $20 for LaptopConnect cards and netbooks; and $10 for tablets and gaming devices.   

Unlike Verizon Wireless, AT&T is not requiring that its customers switch to the new plans when they upgrade to a new device. However, incentives like free tethering and now FaceTime over cellular could be the kind of goodies that will push more customers to the data-centric plans. 

A Verizon Wireless spokesman had no official comment on its FaceTime policy at this time.