From ModMyiFone - Wiki
Software Development
With the iPhone, a whole new world of Mobile Developing has been opened up. The phone runs apps built with a typical Web App format, such as AJAX or PHP. Basically, anything that runs in Safari (with the exception of Flash) will run on your iPhone.
The following is a list of helpful information for developers wanting to code for the iPhone. Feel free to add anything you see fit here.
Application Development
Operating System Development
With iTunes as a flashing program to restore your iPhone at any time it is fairly easy to located the firmware for the iPhone. With firmware modding in the near future we will be able to modify our iPhones to our personal preferences. Think of all the possibilities, from creating our own applications running on the phone to editing the current ones to our liking. Even changing the appearance of the menus is a possibility soon!
Operating System Development