My iPhone 4 has been upgraded to iOS7 however it won't now log into any service that requires Apple ID as it has now reverted to my old Apple ID email address. The same happened on my iPad, however the Apple forum suggestion to log out then back in to iMessage and FaceTime cured the issue. This however doesn't work on the iPhone, in fact it won't let me log on to either of these services with my real Apple ID and won't let me log out of iCloud from the old ID.
At the moment I have a pretty OS on the phone without email, iMessage nor FaceTime.... HELP???? :-)