Sony Ericsson Patent shows Camera Zooming using Motion Gestures
Sony Ericsson has filed a patent that allows zooming to be done just by the moving the camera back and forth. According to the patent, a reference object is needed to pre-determine the zoom factor that you want the lens to go. The patent talks about obtaining the output of an accelerometer and utilizing it in the camera zoom function.
Here is a quote from the patent page:
A device may establish a distance of a device from a reference object. The device may also determine a difference or change in the distance, obtain a zoom value based on the difference or change, and zoom in or out on a view based on the zoom value.
You can read about this patent here.