It's incredibly unlikely that NASA would let you control a real rover using an iPhone app but just in case you're wondering what that might look like, watch the video below.
At this year's annual meeting of the Eclipse* open source community (EclipseCon 2010) attendees were challenged to create a robotic control system to drive a NASA-provided robot across a "prototypical Mars landscape". To win the EclipseCon e4-rover Mars challenge, developers could either prove their e4 programming skills by creating the best e4-Rover client, or use an e4 client to operate the Rover through a series of tasks to collect points.
Software architects Peter Friese and Heiko Behrens built a very cool iPhone client for the EclipseCon challenge which controls the robot around NASA's Mars landscape. As you can see in the video, Friese and Behrens Mars rover iPhone app works using the accelerometer. We love the fact that these guys were still competing at 3:45am but when the prize is a visit to the NASA robotics lab in Los Angeles, a Lego Mindstorms NXT 2.0 robotics set and $500 credit for Amazon Web Services, it's very understandable.
Update: For more info visit Peter Friese and Heiko Behrens' recently created iPhone Mars rover site.
*In 2003–2004 the Eclipse Consortium, an unofficial consortium of 50 software industry vendors founded The Eclipse Foundation, a not-for-profit legal entity to lead and develop Eclipse.