Audi is using the iPhone to drive interest in the 2009 Audi A4 with the first iPhone app from a carmaker.

Available on Apple's iTunes App Store, the Audi A4 Challenge is a driving game that takes advantage of the iPhone 3G's accelerometer motion-sensor technology to steer a digital version of the new car through a series of increasingly difficult courses.
Customers who visit Audi's truthinengineering.com/a4/iphone on their iPhone can check out other downloads, including videos, wallpapers, an exterior color customizer, a dealer locator and link to the Audi A4 Challenge on the App Store.

The application is free and available now. The A4 is most definitely not free and will be available in September.