IPhone-Rocket-Launcher is a project mainly written in Objective-C, it's free.
Use your iPhone to control a Dreamcheeky USB rocket launcher
Use your iPhone to connect to and control a USB rocket launcher
Contains two examples of using the iPhone to connect to a Rocket launcher server and control the rocket launcher remotely.
Rock - Control the launcher with buttons Very basic app, doesn't support multiple actions at the same time (eg. down-left or up-right).
Rock2 - Control the launcher with the accelerometer Tilt the iPhone left/right (like changing orientation from portrait to landscape) to rotate the rocket launcher, and tilt it to control the up/down movement. This app doesn't support firing yet.