Another new feature coming in iOS 6 will be limited to devices running Apple's custom A5 chip or later, as FaceTime over 3G will only be capable on the iPhone 4S or third-generation iPad.

That means owners of the iPhone 4, Apple's first device to offer FaceTime, or the iPad 2 will still need to be connected to Wi-Fi in order to conduct a FaceTime video chat call when iOS 6 launches this fall. The restriction was revealed in the fine print of Apple's official product page for iOS 6.

FaceTime over 3G joins turn-by-turn directions and the new "Flyover" feature in Maps as functions in iOS 6 that will require an A5 processor or newer. The iPhone 4, first released in 2010, runs the previous-generation A4 chip.

While iPhone 4 owners won't get FaceTime over 3G, turn-by-turn directions or Flyover, they will have access to shared Photo streams when iOS 6 launches this year. iPhone 3GS owners won't be so lucky, however, as Shared Photo Streams requires iOS 6 on an iPhone 4 or later or iPad 2 or later, and a Mac computer with OS X Mountain Lion.

The iPhone 3GS will also miss out on VIP list in the iOS 6 Mail application, along with VIP and Flagged smart mailboxes. Those features will be available on the iPhone 4 or later and iPad 2 or later.

And the new "Offline Reading List" in Safari also requires an iPhone 4 or later and iPad 2 or later, meaning the iPhone 3GS, which was first released in 2009, didn't make the cut.

Finally, "Made for iPhone" hearing aids, a new accessibility feature of iOS 6, will require an iPhone 4S to work, when compatible hearing aids hit the market.