Several users have experienced an issue in which iPhone 4’s FaceTime feature does not work after a phone number is ported from Sprint, Verizon or T-Mobile to AT&T. Users experiencing this problem may receive the error message “(name of user) not available for FaceTime.”
Fix
This issue can generally be resolved by restoring, but not from a backup. It appears that bad holdover data from iPhone backups can cause the problem. Restoring as a new phone will delete contacts and other data, but may resolve this problem.
To do so, first backup your iPhone in iTunes. Next, connect your iPhone or iPod touch to your computer, click “Restore” in iTunes, then choose “setup as new phone.” You can later re-sync your apps and other information.
Obsessed with tech since the early arrival of A/UX on Apple, Sudz (SK) is responsible for the editorial direction of AppleToolBox. He is based out of Los Angeles, CA.
Sudz specializes in covering all things macOS, having reviewed dozens of OS X and macOS developments over the years.
In a former life, Sudz worked helping Fortune 100 companies with their technology and business transformation aspirations.
APPLE FIX
Have you guys tried this:
https://support.apple.com/kb/HT4246