Attempting to add a supported phone to iSync using the Add Device choice in the Devices menu may cause this alert message to appear:
"Your phone (phonename) does not work with this version of iSync. To enable this phone to work with iSync, contact the phone's manufacturer or your service provider to update the firmware on your phone. For more information, visit the iSync Support website."
Update to the latest versions of Mac OS X and iSync via Software Update.
If the issue persists, check with your cell phone provider or manufacturer to see if a later firmware version is available for your phone.