The following hint was submitted a while ago in the comments section of another hint about the 9300. In 10.6, I couldn't get the original hint to work, but the method from this comment worked fine. For others struggling with this in 10.6, here's the method from that comment:
Control-click on iSync.app (version 2.3) and choose Show Package Contents from the pop-up menu. Navigate into Contents » PlugIns » ApplePhoneConduit.syncdevice » Contents » PlugIns. Duplicate the folder Nokia-9300i.phoneplugin, and rename it as Nokia-9300.phoneplugin.I just used it under 10.6 on a new MBP and it worked great.
Open the new folder Nokia-9300.phoneplugin, then open the Contents folder within it. Open file info.plist with TextEdit, find ALL 9300i references and replace them with 9300, then save. Next, open the Resources folder, and rename com.nokia.9300i.tiff to com.nokia.9300.tiff.
Open MetaClasses.plist with TextEdit, find all 9300i references and replace them with 9300, then save. Close all open files and you're done! Happy Synchronizing!
Mac OS X Hints