July 1, Californians will join many other states and countries in requiring drivers to use handsfree devices when talking on their cell phones. I called Bill using the Jawbone today. Listen to the audio here. I currently use the BlueAnt Supertooth Light in my car. It has its own speaker and mic and attaches to the visor. It works pretty well and gets great battery life (as long as you remember to turn it off when you're not in the car).
Here's a recording I made in the same room as the Jawbone recording. It doesn't sound much better, but it's usable.
Another system that requires no installation but uses your car speakers is The Tooth Pik. I haven't tried it and can't offer a sample recording but if someone has one let me know so I can record it!
By the way, there really was a Bone Fone. Here's the original ad, courtesy the Pocket Caculator Show: