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The details on how to create apps for both the FaceBook and iPhone platform are changing all the time. I learned that there are two varieties of iPhone apps. There is the native variety that runs on the iPhone operating system. Then there are iPhone web apps that run on the Safari web browser.
Going a little deeper, you write native iPhone apps using the Objective C programming language. However iPhone web apps are developed just like other normal web applications. You code in a combination of HTML, CSS, and JavaScript.
Finally note that games are the best selling apps. It seems like there is too steep a learning curve to code up an app myself. I think for now I will take a pass on this money making opportunity.