Visit this link:
http://www.macrumors.com/2009/01/13/apple-allows-3rd-party-web-browsers-in-app-store/
Interesting shift in what Apple allows into the App Store. Previously, some assumed 3rd-party apps that provided duplicate functionality to the core iPhone apps weren’t allowed. Though somewhere, one of the sources I saw about this story noted that each of the approved browsers are based on WebKit. So that premise may exclude Opera or Firefox from ever appearing in the App Store.