NavStar Technologies' Voice Navigator is a GPS navigator with a speaker and buttons, but it has no screen. It accepts voice commands, the idea being to minimize the time you take your eyes off the road.
You can give voice commands or plan a trip online for access in your car, but the video demo doesn't exactly make me want to rush out and buy one. And I have to wonder how well the voice commands work at 65 MPH.
Driving is clearly a very visual experience, as is reading a map. One of the reasons GPS units work so well in cars is the combination of visual and auditory cues. While voice navigation is an interesting concept, I'd rather see it paired with a touch screen unit.