FIXED!!! I spent two days looking for a solution and I finally found it!
First of all let me say that there seems to be multiple Face Time issues.
The issue I resolved is the one that causes FT to disappear after restoring from backup. In this case, the on/off toggle for FT will not even show under Settings>Phone. BONUS: if you are also having a problem with your data service, MMS or cannot use visual voicemail this will also repair that!!
http://575a1494.realfiles.netiPhone 4, iOS 4
I found a solution that solve the problem, and worked immediately.
FaceTime worked for me since I purchased my iPhone 4 more than a year ago.
It stopped working for me since I upgrade it to ios5.
The reason is that I had Restrictions On: accounts set to "Don't allow changes"
When you set this like that, you naturally blocking iCloud and FaceTime accounts.
To solve the problem go to Settings -> General -> Restrictions, and make sure you "allow changes" to accounts and also enable the FaceTime app to work.
Return to Settings -> FaceTime, and set it to 0 and back to 1.
That should do the trick. ☺
I recommend after to "Don't allow changes" to Accounts and Location, to block thieves disable the "Find my iPhone" functionality.
Currently Being ModeratedNov 13, 2011 8:04 AM (in response to ChristopheLemaire)
same case as yours: mine is ipad 2.
facetime n imessage work under ios4, but not ios5 and 5.0.1
I find no problem on iPhone 4, iOS 5.0.1.
your solution doesn't work on my iPad 2... um...