Dark Knight app for the Apple iPhone starts as free preview and can end with you downloading the full-length film
You will be given the choice to download the movie onto your Apple iPhone ($10) or have it streamed to your phone ($12). Unlike the version of the films that you might download from iTunes, the version of the film that you purchase from the app contains some extras like the ones you might find on a DVD release of the movie. And you can watch your films on either Wi-Fi or 3G.
For Warner Brothers, distributing the two movies this way allows them to be viewed by iPhone users in 35 countries vs. the 12 that could buy them through the iTunes Movie Store. And Warner Brothers expects to release more movies as apps later this year.
source: Apple iTunes (1), (2) via 9to5Mac