As far as I know it is someting to do with the phones OS (=symbian) and the bluetooth.
I do have a N70 with symbian and I've managed to do something about it: there is a Nokia application (I downloaded it from w w w.nokia.es/A4181551 ) that once installed and ran
from your phone, will transfer the phone book to the car. What I am not sure yet is if it will keep it syncronised when you add new entries.
hope it helps!