On a whim (and on a nudge from MobileLab) I downloaded the VoiceBand for iPhone app. I think this will be fun as soon as I can actually get some time to play with it. Here is a quick sample I made while sitting in my car. This is the sound of my car on idle, as played by the bass guitar simulated instrument in VoiceBand.
I wonder what it would be like to record random city noises and assemble them in to some sort of hodge podge song. Perhaps something like what Mona Kasra has done with Daily Tones.