I joked just the other day in my blog entry titled: McDonalds VoIP, Fries with your VoIP? that GM should offer VoIP in their cars in conjunction with their OnStar system so you could make VoIP calls (car-to-Skype, car-to-SIP URL)
I guess they'd have to add "Driving" as a new "presence status" to the "Away", "Out to Lunch", "Offline" list. If you integrate it with the speed, you could see "Driving 135mph" - a perfect time to make an inbound call to this car if you want someone to crash... I digress...
Well, ironically just two days after my GM Onstar/VoIP idea, Nissan announced a major VoIP deployment.
Actually not in their cars though - just their facilities. Newsworthy stuff nonetheless. Check out the VOIP Passes Nissan Road Test eWeek article