Now that I've used it for a few weeks, I can say that I love it. It allows me to use any set of headphones (or other mini-jack) with the iPhone which is quite nice since Apple crippled the jack to begin with. The microphone feature also works quite well which is a definite bonus. The little button on the microphone can be used to play/pause music from the "iPod" in the iPhone - I wish it had more controls like going forward a song or rewinding by one. That would be a lot of little buttons on the mic, though.
Shure MPA-3C Music Phone Adapter