I tried it once and it worked fine, as long as you were in range of a strong FM station.  As you drive further away, and lose that station, you lose the MP3 playback.  So...if you're near an FM station it works great. I live in a suburban area so it didn't work great for me.

Description

Griffin iTrip Auto Universal Plus Fm Transmitter for iPod iPhone Smartphone 
  • Compatible With Any Portable Audio Device With A 3.5Mm Headphone Jack
  • Charges Any Portable Device With A USB Port
  • Built-In Antenna
  • Powered By 12V Power Outlet
  • FM Stereo Modulation
  • Listen to your MP3 or other portable player on your car stereo
  • 12V power plug works with any cigarette lighter socket
  • Simple 3-step setup
  • Lighted display is easy to read
  • Built-in USB port lets you charge your player using your own charging cable
No international shipping.