We're supposed to hear more about the AR.Drone at E3 in a few weeks, but you may not have to wait that long -- Flypad is an app coming soon to the App Store that purports to let you fly any RC-controlled plane with an iPhone, just by connecting the iPhone's audio out signal up to an adapter. The iPhone can even be connected directly to a PC with the use of special RC simulation software, and from there you can use the dual-joystick setup to control any other games or software.
It's not an all-in-one solution like the AR.Drone (and the controller is just that, no video or special AR included). But if you already have a plane and a transmitter that's compatible with this setup, the app could be a cheaper way to use your iPhone as a controller. No price yet, but the app is under Apple's review right now.