installing the dmg is only one step. you also have to copy icons for the phone in the folder:
Applications/iSync.app/Contents/PlugIns/ApplePhoneConduit.syncdevice/Contents/Pl ugIns/ _PhoneModelsSync.phoneplugin/Contents/Resources/
you will find some there:
http://www.resilion.be/kenny/stuff/noks80icons.zip
in addition you have to change code in the file MetaClasses.plist
you will find guides on google. i have it only in german.
after that you have to set up the phone with bluetooth and after this connect it in the adressbook also with bluetooth. when you start isync and search for your 9300 it should work.
for connecting your mac with the modem of the phone you need drivers
http://www.taniwha.org.uk/files/NokiaGPRS2004-05.sit
http://www.taniwha.org.uk/gprs.html
copy them to /Library/Modem Scripts/
i have not tested it.
marcus