Having not long got an iPhone 5s I was struck by the potential for mishap - particularly in my butter fingers - while using the camera, especially for shooting video.
There are various hand grip type mounts and even steadicam type assemblies available to aid the iPhone videographer, but they tend to be expensive. There is AirClip, which I found after setting out my design, but seems only available on Amazon US.
I will confess I used the downloadable iPhone 5 case that Shapeways make available
here, and added the rings to the model.
The rings are placed so that your thumb is right over the on screen shutter release button.
This prototype needs some work however, particularly to make the frame stiffer in the horizontal axis; the phone does wobble quite a bit and the frame flexes enough to allow gravity to do its dirty work.
Apologies for the dull outdoor shots; it is, as they say around here, a rather dreich day...