First of all, it took me quite a while and many increasingly frustrating attempts to add the N900 to iSync until I had figured out that for Bluetooth synching I first need to enable Bluetooth Dial-Up Networking on the N900 by installing bluetooth-dun from Extras. After that, and after installing the community provided iSync plugin, iSync recognised my N900 just fine and synching works nicely now. I'd like to take this opportunity to thank those who provided the plugin! I also tried the official Nokia plugin, but couldn't get it to work. It recognised my phone alright, but gave me an unspecified error during synching.