Google just announced a new beta AdSense program that allows developers of mobile applications for iPhone and Android. Now, approved applications can make on-going revenue with advertisements through AdSense.
Currently, it's not open to just any developer -- you have to have an application that gets over 100,000 page views per day. In addition to that, the new program is available only for free applications -- thankfully double dipping isn't allowed.
Applications accepted into the program are also locked into a 3 month contract, and must be implemented withing 4 weeks.