If you're using the Finder to navigate to the directory, you need to ctrl or right click on the iSync.app and choose "Show Package Contents".
Now, remove all the current definitions of your K750i in the bluetooth preferences and ~/Library/Phones directory. Reconfigure your phone and you're all set to go.
Update 1116669672 - On initial sync, select 'Merge data on computer and device' or the sync process will fail and you have to 'reboot' your phone Update 1116673200 - I've only been able to test this on Tiger, so I have no idea if this will work on earlier versions of Mac OS X Update 1116677692 - To show you the 'quality' of the built-in 2MP camera, I made picture of Heimlich using the macro option. Und Heimlich, Nokia 6230 style Update 1116694607 - Added two images of the K750i ( thanks to Julian Wright ). Don't forget to download the new MetaClasses file Update 1116716466 - Added some external links at the bottom. Including Stefan Lindmark's site which explains how to get it to work on Mac OS 10.3 Update 1121507506 - Apple has released an iSync update which now supports the *750i phones. Get your fix now !!