Techcrunch has this great little post, Just Four Dudes Jamming On The Subway — With Their iPhones As Instruments.
You know what I find most astounding about it? Not so much that they're using phones (I've been to multiple concerts which used phones as instruments ), but that they conceived this stunt, brought the equipment on a train, and were able to just do this. No one called security, freaking out when they brought speakers on board, even though the person quoted there said that was her first thought.
Here's the video:
Amazing what a real band can do with what's on hand, eh? Now I want to perform random acts of music using all that computing power that fits in my pocket. The phone's a whole lot easier to carry around than my guitar, and a lot easier on my fingertips... Anyone want to work on some tunes?
 My personal favourite was Danny Michel at Westfest a few years back. He performs by himself using a loopback device and often doesn't make much deal of it (in fact, I've been with folk who didn't notice) but for one song he laid down the intro using the beeps of an older cell phone, and worked that into the mix that was repeating throughout. It fit incredibly well with the fact that he was singing a song heavy with nostalgia ("In Full Effect").