For those of you looking to turn your iPhone into a full-fledged music studio, there is the new iDiscovery
keyboard and app from Ion Audio
. The iDiscovery has 25 keys (2 octaves) for playing, specific synthesizer keys with 2-dozen MIDI samples, and pitch and modulation wheels. What's interesting is that the top of the keyboard has a cut-out for you to place your iPhone when connected, but the keyboard appears to lack any internal speakers, so you'll have to connect a pair via RCA out, or by using headphones. You can also connect the device to your PC and Mac via USB so that it can be used by any MIDI software you may have. Expect the iDiscovery to be released by Q2 2010, though pricing has not yet been made available.
source: Ion Audio