With the growing market for portable, mass storage audio players, there is an obvious use that seems to be nearly overlooked. Sure you can carry 40 GB of music in your pocket, but if you're driving in your car how do you listen to it without a pair of headphones. Aside from being illegal to wear while driving in most places, headphones sacrifice the sound quality of that high end car stereo system you've installed as well!

The ideal way would be to plug your iPod or other portable music device directly into your car stereo, but then very few offer an auxiliary input, and very few of us still have cassette decks in our car to use that type of adapter. This leaves us with really one option, barring the purchase of a new stereo deck with an aux input, that option is FM modulated transmission.