Thus the "only devices that support audio only calls." It may also support the Mac OS X FaceTime app if it gets an update. However, looking at how FaceTime works and how the OS X and iOS versions of it get their settings and updates almost dynamically from Apple, it could be enabled on all devices once iOS 7 is released. All Apple needs to do is change a boolean value in the configuration file FaceTime downloads automatically every few days to yes/true and it'd work. The value's name is "AllowAudioOnlyCalls". A boolean value that's been in the FaceTime settings since iOS 4.0.