http://support.apple.com/kb/HT4246 ----- Summary After porting your number or installing a carrier settings update and attempting to use FaceTime on iPhone 4, FaceTime may exhibit one or more of the following symptoms: * When you are calling someone on FaceTime, the number on their screen is not your number. * People are unable to initiate a FaceTime call with you. * After installing a new carrier settings update, FaceTime does not activate. ----- To resolve this issue: * Use iTunes to update to the latest version of iOS for your iPhone. * Disable FaceTime in Settings > Phone and then turn it on again. Do this by sliding the slider off and then on. * Reset All Settings under Settings > General > Reset.