Sometimes your iPhone freezes and looses information. As example the SMS database. I've had some freezes in the SMS application which resulted in an empty SMS database.

Luckely enough, iTunes makes an backup of your iPhone, everytime it syncs. This backup contains preferences, notes, SMS messages, call history and photo's.

When you're in a situation where the iPhone lost, for example, the SMS database, DON'T sync, but just remove the following folder:

/var/mobile/Media/iTunes_Control/iTunes/
 

Now connect your iPhone again with your mac, iTunes will detect the iPhone as a new device, and asks you if you want to restore a previous backup.


Click "Continue", your iPhone will be restored to the previous databases and settings, while keeping your applications etc.