onOne releases a cable release DSLR Remote application for the iPhone. It allows you to control (Canon only) DSLR cameras, wirelessly from the iPhone. Hooking up a Canon DSLR camera to a computer via USB, allows the DSLR Remote to communicate with the computer. You can then use the application to control the camera's shutter speed, aperture, white balance, etc....
You can even see the camera’s Live View right on the iPhone, giving you a real-time preview before shooting your photos. The Pro version is in the iTunes store at an introductory price of $9.99 and will jump to $20 shortly after a brief period. The lite version, limited to shooting photos only, sells for $1.99. If it sells well, we can no doubt expect a Nikon version, if not already in the works. Check out their site for more info, and camera compatibility.