Had the THB Bury universal car kit hard wired (i.e. when the phone rings it cuts out the radio/CD and voice is conversation is through mic above head and car speakers).
When the company change the phones - all I have to do then is change the adapter cradle that sits in the car kit. The 8100 example is on this link Blackberry 8100 Pearl Cradle
But plenty of companies offer it I believe