Wenn das iPhone nicht mehr mit iCal synchronisiert gibts hier EINE mögliche Lösung, hat bei mir geholfen.

Reset the SyncServices folder with these steps in Mac OS X 10.5:

Open iSync.
Choose Preferences from the iSync menu.
Click Reset Sync History.
If this does not resolve your issue, or if you are unable to open iSync, follow these steps:

In the Finder, choose Utilities from the Go menu.
Open Terminal.
In the Terminal window that opens, type or paste the following command on a single line:
/System/Library/Frameworks/SyncServices.framework/Versions/A/Resources/resetsync.pl full
Press Return.
When the operation is complete, quit Terminal.