Cant Turn on Facetime Option iPhone 4

Hi, I have a situation that I really dont know how to resolve, I have been using iPod Touch since the second generation and Ive been using the backup to restore everytime I buy a new iPod Touch.
Now, the last iPod Touch I bought was the 4th generation 32 GB, with that iPod on iOS 4.1 I enabled the FaceTime account with email address and it worked normally.
Two days ago I got my new iPhone 4, it is on iOS 4.1 and I restored it as always, with the backup of my 4th gen iPod Touch, all worked normally.
The problem is this: I cant enable FaceTime now, I go to settings>phone and there is the on/off toggle for FaceTime, but here is what happens, I turn it ON, but when I go back to the homescreen the toggle return to OFF position by itself, Ive tried reset all settings and restarting the iPhone but same happens, I think there is some kind of conflict because the iPod Touch 4th gen works with e-mail and maybe the iPhone cant read that or something like that. As a new iPhone the on/off FaceTime toggle works normally on the iPhone.
I need a way to reset the FaceTime settings but the only impossible option for me is restore as new and loose the backup that Ive been using for a very long time that has a lot of information and work.
Please help me!!
iPhone 4 iOS 4 4.1