I haven't done much research into integrating a CarPC with BT but I'd imagine the possibility of pairing your phone to your computer to make calls is possible, seeing how Garmin and other companies do it with their GPS units.
I'm not sure what you're trying to get at with the whole new address on the fly bit, but there is an on screen keyboard so you can do just that
(in iGuidance). I believe people also have integrated on screen keyboards into the operating system. There's a whole mess of the stuff @ mp3car and the possibilities are endless.
But in the end, it's your call
The only thing that concerns me is that the Jensen may be low quality.