One of the new iPhone apps that was demoed at the iPhoneLaunchParty last night was bChamp by Monodomo. bChamp is a beat-boxing application that allows you to use your iPhone as a beat-boxing device. It's hard to describe so we'll start with this developer video that shows you the basics:
http://www.youtube.com/watch?v=Xwzi2vyj59M
The pitch of the sounds can also be changed by moving your finger on the screen. Steve Wozniak was at the iPhone Launch Party and tried his hand at bChamp:
http://www.youtube.com/watch?v=hd8HwmFZuaE
bChamp is available in the App Store for $0.99.
App Store Link: bChamp, $0.99
Article Link: bChamp: Beat Boxing App, Steve Wozniak Gives it a Try