MacRumors first reported the FaceTime connectivity issue, and notes that some of the users have reported problems on the Apple Support Communities page. One of the users on the Apple Support Communities said, "Since today FT [FaceTime] stopped working on my mother's iOS 6 iPad and iPhone. I've tried calling with an iOS 6 iPod and also got 'FaceTime Connection failed'. Same when I tried to call from an iOS 6 iPod to my iOS 7 iPhone. From iOS 7 iPhone to iOS 7 iPad things are ok. Could it be that Apple made some service change that killed iOS6 FT compatability?"
Another user wrote, "I have the same issue since Wednesday. I think it is related to iOS version. I have devices on various iOS versions - 5, 6 and 7. It only works for me when FaceTime from iOS 7 to iOS 7 device. All other connections failed. Probably, just wait to see if Apple can fix the issue soon."
MacRumors claims that Apple representatives are recommending an update to iOS 7 to fix the FaceTime connectivity issue. As of now however, Apple has not acknowledged any FaceTime connectivity issue on iOS 6.