Coinciding with the problematic launch of pre-orders for the iPhone 4, Apple has launched an official, free Apple Store application formatted for the iPhone and iPod touch, but also compatible with the iPad. The application is designed to let customers “buy Apple products and accessories, read customer reviews, find an Apple Retail Store, stay up to date with in-store events, and make Personal Shopping, Genius Bar, or On to One appointments,” and is billed as “the easiest way to buy or reserve your new iPhone—right from your current iPhone.” It also uses push notifications to provide updates for as yet unknown purposes.

Like the Apple Store web site, the application’s main screen currently displays a “We’ll be back soon” post it note graphic, seemingly related to the iPhone 4 ordering outage currently affecting the Store. Screenshots show the application offering five bottom-of-screen buttons to toggle between Featured, Products, Stores, Search, and Cart screens that are not yet available. This is Apple’s fourth separate selling app for iOS devices, following iTunes, App Store, and iBookstore within the iBooks application.

Update: The Apple Store app became functional shortly after 9:30AM. It notably offers iPhone 4 pre-ordering only for existing iPhone customers who wish to replace current iPhones with iPhone 4 models, and only reservations for customers who intend to create new accounts or add lines.