A year ago, I bought a Logitech Freepulse Wireless Bluetooth Headphone to listen to my music without getting in trouble with cables.
Normally you need the headphones and a little bluetooth box you plug into the audio device. With the iPhone 3G and 3GS, Apple added the A2DP protocol to listen to music using Bluetooth.
There is a way to use your Freepulse without the little box. Just push the ON button on the headphones for 15 seconds. Wait for the light to flash in blue and red. If the light is flashing, you can easily connect to the headphones from your iPhone.