If you have a Symbian OS-based phone and try to sync it with your Mac shortly after changing some information on the phone, the recently entered or modified data may disappear from the phone and won't be synced to the computer. This can happen if you're using iSync 2.0 (included with Mac OS X 10.4 Tiger).
To avoid this issue, wait 1 or 2 minutes before syncing if you recently added or modified contacts, calendars, or to-do items on the phone. After waiting, you should be able to sync normally.
Important: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.