Fixed quote from this post:
http://discussions.europe.nokia.com/discussions/board/message?board.id=pcsuite&message.id=18480&view=by_date_ascending&page=3
To get the iSync to work with the Nokia 6120 Classic:
Download the plugin from
http://the.taoofmac.com/media/Nokia/6120/Nokia-6120c.phoneplugin.zip
(mirrored here) and unzip it.
Now find iSync (it should be at your Applications-folder), right-click (ctrl-click if you have an one button mouse) on it and select ‘Show Package Contents’.
Navigate to Contents > Plugins > ApplePhoneConduit.syncdevice > Contents > PlugIns and drop the ‘Nokia-6120c.phoneplugin’-folder into this PlugIns folder.
Now unpair the mac from the phone (if you have already paired them) and re-setup the phone using Apple’s bluetooth utility.
Start iSync and the phone should come up automatically. (Actually the iSync will start automatically, when you finish the pairing-process)