The Jupiter Jack
The Jupiter Jack is a neat little gadget that you can plug into the audio jack on any cell phone. You then tune your car radio to 88.7 and you now have a hands free cell phone that you can hear through the speakers of your car!

The idea is good, and the Jupiter Jack has been successful, however I would be cautious in buying one of these. If you have ever plugged an iPod or other MP3 player into your cigarette lighter, and tuned your radio to the right station, you have probably experienced the frustration of the constant background static. You would have to get awfully lucky to get clear reception through your speakers with the Jupiter Jack.

You can also purchase a wired product that can be installed in your car's auxilliary which will produce a perfectly clear sound every time. The benefit to the Jupiter Jack is that it has no wires annoying you while you drive. (although the wired ones can be installed internally, so that no wires are showing)