Lost my FaceTime capability after jailbreak.
UPDATE: You can work around by doing a backup first, jailbreaking, and then restoring from backup (which just copies settings/etc over). Stays jailbroken. If you have a pre-jailbreak backup apply that to fix.
chmod 755 /private/var/mobile/Library; chmod 755 /private/var/mobile/Library/Preference after that Reset Network Settings
Full restore failed for me. I'm trying this procedure: http://forums.macrumors.com/showpost.php?p=10298203&post...
Talent does what it can, Hackers do what they must :)
(Apologies to Edward Bulwer-Lytton)