One of the biggest problems with music apps on iPhone is the lack of Camera Connection Kit support from Apple. This prevents you from using USB devices like MIDI keyboards or a recording interface. A Cydia (Jailbreak) App released today will let you do both!
CameraConnector (available on repository BigBoss for $1) says it only works for HID USB devices, like mice and typing keyboards, but MusicApps.com.br reader Giusoares has got it working with a lot more!
Googlish + Me Translation:
I've confirmed my USB devices are recognized:
Tascam us 800 USB
MIDI USB universal
Behringer USB stereo interface
Guitar Link USB
Today during the day I will do recording tests to see how they behave, demonstrating the novelty. I'll make a video to show you guys. I did the test on the iPhone 4.
Awesome news for iPhone musicians! Note that this only works on iOS 5.0+. Let me know if anyone gets this working on USB-MIDI keyboards as well. I assume it should, if the MIDI-USB adapter did.