The fairy tale continues for Apple users subscribed to AT&T, making full use of the FaceTime feature.

Per reports, U.S.-based mobile subscriber AT&T has now started allowing customers on any compatible device to video chat while on a mobile network, and this is irrespective of whether the user is in possession of a LTE-capable device or not.

Basically, AT&T is extending the popular FaceTime over cellular to any compatible iOS device on a tiered data plan. Now, as planned, over the next couple of weeks, the company will start rolling out the newest option to people with compatible iOS devices like the iPhone 4S, provided they are on tiered plans rather than the unlimited ones. However, the entire expansion is expected to take a few months.

"As a result of ongoing testing, we're announcing AT&T will enable FaceTime over Cellular at no extra charge for customers with any tiered data plan using a compatible iOS device," said Mark Collins, Senior Vice President, Data and Voice Products, AT&T.

"This means iPhone 4S customers with tiered plans will be able to make FaceTime calls over the AT&T cellular network. AT&T previously made FaceTime over Cellular available to customers with a Mobile Share plan and those with an LTE device on tiered plans."

Collins said AT&T has already started updating its system and will begin rolling out FaceTime over cellular to more Apple devices in the next couple of weeks.

"We have already begun updating our systems and processes and expect to start rolling the update out to customers on an ongoing basis beginning in the next couple of weeks. Customers do not need to do anything-the update will be applied automatically over the next few months," Collins added.

However, interested users need to note that although the iPhone 4 and iPad 2 are compatible with FaceTime, none of the devices can use the service over cellular connections. The FaceTime is only compatible with iPhone 4S, iPhone 5, third- and fourth-generation iPads with cellular, and iPad mini with cellular.

FaceTime first arrived on the iPhone 4 back in 2010. At that time it was limited to Wi-Fi-only connections, and, accordingly, AT&T points out, "FaceTime over Wi-Fi remains available for all customers who have a compatible iPhone or iPad."

FaceTime was actually limited to Wi-Fi connections for subsequent devices running iOS 5, including the iPhone 4S, iPad 2, and iPad 3.