writes: Apple's stepped up rejections are helping to foster competition in the app store marketplace. According to an article by Wired, developers aren't taking AppStore rejection lying down, but are turning to the hacking community's repository system for the iPhone to launch an app store of their own. The Cydia store is yielding notably higher sales for some application developers than Apple's AppStore, and is reportedly running on over 4 million Apple iPhone devices. In this store, developers are distributing applications they've written that push the limits of Apple's normal AppStore policies, with software to add file downloads to Safari, trick applications into thinking they're on WiFi (for VoIP), and enhance other types functionality. You'll also find the popular Google Voice application, which was recently rejected by Apple. Third party application development has been around since 2007, when the iPhone was originally introduced, and became so popular that a book was published by O'Reilly Media specifically geared toward writing applications before an SDK was available. The Cydia store acts as both a free package repository and commercial store front to third party developers.