This statement from Nokia may make your retro install arguments null and void? Unless you hurry...
****
As from the end of June 04, stocks of the Nokia 6310i mobile phone will no longer be available as Nokia will withdraw this handset due to it coming to the end of its product lifespan. Unfortunately, none of the new Nokia products coming along to replace this product will fit this existing accessory suite. This includes the fully installed cark91. Nokia’s rationale for making the switch is to allow their new devices to benefit from new technologies that are available today and that these require different connectivity into the handset.
****
I guess it depends how much you want the 6310i/bluetooth capability. Get it now if you really want it. I'd love to know what's replacing it as their main 'business' model. I was just about to upgrade from my 6210 but I'm going to wait and hope the new one is an exciting development.