function worthless for me...doesn't work at all in my car plugged in or not (2008 BMW). I think the radio antenna is in the "shark fin" on the roof (meaning steel barrier in the form of the roof between the N900 and the antenna) and the rest of the RF path is exceptionally well shielded...so there ya go. Maybe if i open the sun roof, duct-tape (or "90-mph tape", as is appropriate) the N900 to the roof it might work

Not a huge issue...the car has both aux port and usb port...but it was a little disappointing that this little gadget feature didn't work.