When I got my G5 I was quite frustrated to know that my Nokia 6230 was not supported by iSync and OS X Tiger (neither was the Nokia 6320, as many misspell it :-D). I the current iSync version (2.2), altough, the support has been added!
Unfortunately iSync was still reporting the phone as unsupported. After reading this thread on how to use iSync and the Nokia 6230 with an old firmware I found that the phone synchronizes perfectly. Just for your information, the firmware version of my phone is 04.28 which is probably a very old one since I bought the phone when it was quite new on the market and I never updated it.
Since now I can sync iCal with the phone, I also have found a nice php script that helps me to publish iCal to my web server so that I can still check my calendar even if I don't have my phone with me. Actually, iCal can push your calendars to a webdav server natively (in its own text-based format). What you need is only a script to render the calendar in a nicer way.
I'm also looking for a way to publish the AddressBook so that I can access it from work. plaxo.com provides a nice solution, which is also portable to other platforms (I run Windows at work) but I just don't like the idea of committing to a commercial service, altough they offer their base account for free (for how long?)