When Angela LaFollette reviewed Orphion back in February she seemed to enjoy it quite a bit, and now a similar abstract music-creation tool is available for the iPhone by way of orphinio.
I say "similar" because it's not actually Orphion with a different screen resolution but rather a separate app. The sound is a little different as well; the developer states it's sort of like a combination of a jaw harp and a glockenspiel. You can nab this surreal little digital instrument for $0.99.
◦ Different articulations from soft to plucked to hardly slapped
◦ Natural interaction
◦ Shaker mode
◦ Individual voices for each finger
◦ Extend your ways of expression as a percussionist, guitarist, pianist or other musician
◦ 9 transposable pad layouts with different tonalities from easy to complex
◦ Record and share what you play via EMail, SoundCloud or AudioCopy
◦ Audiobus support: Now you can stream live audio directly to other Audiobus-compatible apps!