To find the MetaClasses.plist file, control-click on the iSync application and select Show Pacakge Contents from the pop-up menu. Navigate to Plugins -> ApplePhoneConduit.syncdevice -> Contents -> Plugins -> PhoneModelsSync.phoneplugin -> Contents -> Resources, and in that folder you will find MetaClasses.plist. Before you start changing stuff around, my advice is to make a copy of your original file and name it MetaClasses.plist.old or similar.
Now here's the kicker ... for whatever reason, the file uses the MOTV3-black.tiff icon. So I just deleted that one, and used a new one I made. You can find a lot more on this topic in this thread at howard forums.
[robg adds: This previous hint explained how to add basic iSync support, but without Bluetooth.]

