The iTurn allows you to control a servo via the iPhone’s built in accelerometer. This looks really easy to do, and it could be used in a lot of different projects. Check out the link for more information.
The iPhone or iPod Touch has an accelerometer that detects how the device is oriented. As the devices moves off axis (from straight up and down) the screen rotates. I want to use that feedback to control the position of a motor or servo or cause specific events to happen depending on the device’s position.
More about iTurn: Turn a servo with your iPhone