There’s an interesting (and free) resource if you’re interested in learning how to program the iPhone- how about a class from Stanford University including video lectures, pdf’s of lecture materials, and other reference materials? The class web page can be found here: Stanford iPhone Class
Stanford actually offers many free classes via Apple’s iTunes U program and a summary of these classes can be found here: Stanford iTunes classes. All you have to do is subscribe via iTunes and you get access to a wealth of materials.
The iPhone development class has been offered for a while and is very popular (millions of downloads). I’ve downloaded the first couple lectures and found them very interesting and a great way to expand your knowledge with only your time investment. One catch- in order to actually work the assignments you need access to a system running MacOS 10 and the iPhone SDK (free from Apple’s developer site). You’ll also have to learn a new programming language (Objective-C). A summary of the steps can be found in this article: 8 Steps to iPhone Development.
There is a .NET development environment called MonoTouch by Novell, but this does cost $399, a convenient (albeit expensive) alternative for Microsoft developers which still requires a Macintosh to do the actual development.
Give it a try and maybe you’ll develop new skills or create the next great iPhone and iPad application.