iPhone Music Studio: Intua releases BeatPack for FREE and Docs online and Tha Bizness shows you how to make some music!
Beatmaker - The Music Creation Studio for the iPhone I wrote about here, has been very popular since it release.
Intua has now released BeatPack version 0.8 Beta. BeatPack is a free MacOS X/Windows tool which enables you to share your audio material with BeatMaker and create compatible sound kits easily. They had also uploaded the docs online. Link.
The producer Henny from Tha Bizness has done a video showing how to do some music with it: