In iSync, you can choose what information is synced on each device. For example, you might want to sync only contacts on your phone or you might want to limit the information synced to speed up the sync or to limit the memory used on a device.
Select the device icon in the iSync window, and then choose the information you want synced on that device. (If the device settings aren’t visible, click the device icon again to expand the iSync window.)
To sync just a portion of your address book to your phone, create a group in Address Book that includes only the contacts you want to sync. Then in iSync, choose to sync only that group. (You can only sync contacts whose information you’ve added to Address Book.)