The iPhone may be a $400 uber-phone, but it can also be hacked and used a music sequencer.

Here, tn800 demos using supercollider and an iPhone to recreate some classic electronic pop:

Here, masayukiakamatsu demos using and iPhone to control Max/MSP:

Here, cappelnord demos a step sequencer for jailbreaked iPod touch, inspired by the Monome 40h Controller:

Another interesting iPhone music experiment is BeatPhone:

Another iPhone electronic music app under development is iPhone Synth, which is currently in alpha.