First of all, this was not my idea. The inspiration was from GeeZuzz (I hope I got that nick right!) who figured out the big idea but it took several weeks of hacking to get the iPhone details working so I take a little credit too.
Download a copy of the Listen beta. It’s still *very* beta. Install it on your iPhone, get near music and run it. It will sample the music for 5 seconds and then attempt to contact the id server. If it succeeds, great, you'll see the song, artist and album. If it fails, nothing happens. You just wait 30 seconds and if you haven't gotten an ID, quit and restart the program.