Check this out, I just saw this on the iPhone app store:
[URL]http://www.simplifymedia.com[/URL]
You can install this on OSX, Windows, Linux and on your iPhone.
You can add up to 30 friends and can stream each others music for free. I just tried it between my iPhone and my linux box at home and it worked easily, it is pretty bad ass.
The first 100,000 iPhone downloads are free, then it is $3.99, but the other versions are always free.
Check it out, maybe some of us on here can add each other, looks pretty sweet!