Iphone Hacks: Pushing the Iphone and iPod Touch Beyond Their Limits
David Jurick, Adam Stolarz, Damien Stolarz
This is over a year old, only covering through the 3G. But the principles he lays out are still valid, and he makes them clear. He refers the reader to websites and programs you can use, which have since been updated for the most current models. As an introduction to the idea of hacking an iPhone or iTouch, it's clear and encouraging.
