The latest update to Mac OSX 10.5.3 now includes inbuilt google/address book synchronization.
However - after updating and adding my login details for gmail to addressbook it just seemed to hang with:
Can't connect to the sync server: NSInvalidReceivePortException: connection went invalid while waiting for a reply ((null))
The solution was to remove the contents of
~/Library/Application Support/SyncServices/Local
and try again.
Note that for account name it needed the full e-mail address complete with googlemail.com domain.
Update
The n95 from nokia is not directly supported by mac osx. However - there are two additions that will help.
iSync
Nokia themselves provide an iSync plugin that will give you full syncing of iCal and Address Book. More info available from Nokia
Address Book pairing