One of the most effective, albeit drastic, iPhone troubleshooting measures (as listed in our 4 Rs) involves restoring the device, but not from a backup. It appears that bad holdover data from iPhone backups (especially those created for previous iPhone models) can cause various issues. This can be accomplished by connecting your iPhone or iPod touch to your computer, click “Restore” in iTunes, then choose “setup as new phone.”
Unfortunately, setting your phone up as a new device will eliminate various important data. As such, Apple has posted a Knowledge Base article that includes steps for preserving these data through the restore process.
The article, entitled “How to back up your data and set up as a new device,” offers tips for preserving purchases, pictures and videos, POP email, SMS and MMS.