IPhone Shopping Cart App interfaced with OSCommerce

We need the development of an iphone app that would connect with our online oscommerce store. We don't want a website browser format, but instead a navigation through the categories and products. The application should pull from the existing online store the list of categories and products, caching it locally. This cache should be updated daily or through a specific user request. The cache should include the product name, description and thumbnail image. App user should be able to navigate through the tree going back and forth and looking the picture & description. Price should not be displayed at this point. Every time a product is displayed, a button "Buy it now" should appear. If the customer clicks on it, it should go into the oscommerce shopping cart operating the same way as through a standard oscommerce purchase. But instead of giving the traditional html result, the app should have inside of it a specific icon to review & edit cart. This icon should only be visible if there items on cart. Checkout should also be done through the app pulling the configuration parameters and using what is set on the oscommerce. Payment will be usually through paypal or our c/c gateway (payflowpro). Obviously checkout can only be available if the app is online with the oscommerce site. We would like to repeat that this is not about creating a different html page for the iphone. We want our own app to have all functions built-in. It possibly will use XML or any other proprietary to talk on the back end between the site and the phone. Since our goal is to sell our products listed on the catalog, we plan to offer the app free of charge. We foresee the need of a few scripts to be added into the oscommerce site that will interface with the app. It is important to implement security in all aspects to avoid code injection and other url spoofing attacks. We should receive the complete source code of all scripts and the full app properly organized and documented.