O’Reillly just published a book by Jonathan Zdziarski, the writer of NES.app for the iPhone and one of the premier iPhone hackers. It describes how to jailbreak and install BSD applications and program using the iPhone APIs. Interestingly, this book assumes that the SDK will be a completely different animal and separates this “open” hacking from officially sanctioned hacking. It looks like a great way to get some iPhone experience before the SDK drops, ensuring you get a space at what is looking to be a pretty crowded table.