01/13/11: As far as I know, no one has been able to find a way to send them all at once, although its been discussed in other threads so you should probably do a search and see for sure. I don't know if this would work since I have no way of testing it but you could also try exporting your contacts into a file on your SD card, then using Astro File Manager to transfer it. Find the file on your SD card in Astro, long-press on the file, press Send, Bluetooth and send it to the car that way.
bigweb, I've answered your other thread. Please don't post the same thing in multiple places. It gets confusing trying to help you. Thanks.
EDIT: 01/14/11: And.... we have found the answer! It may be vehicle-dependent but can't hurt to try it. How to send Contacts to a vehicle using Bluetooth