Churches that fancy themselves relevant, missional and/or emergent either already have an iPhone app or are working on one as we speak.
These churches are very excited about their apps. Some church websites explain that they are embracing technology the way the Apostle Paul embraced technology to spread the gospel (breaking technology being the Roman road system), and the printing press was a technological advancement that was used to print the Bible, then came amplification systems and stadiums and Billy Graham crusades, so the iPhone is a natural progression of state-of-the-art gospel mongering. Some sites also add that their Church App is "a powerful, flexible solution for reaching people in a fresh way." Christian culture is all about the fresh approach.
The church app has everything that the church website does so a smartphone can just as easily go to the church website on their phone even without an app. Then why make a church app at all? Maybe then the relevant church wouldn't have a new media ministry project to herald and assign task leaders to and throw money at. But who really knows.