This is a design I put together for an iPhone passive amplifier. Here is the process I used to create the model in Solidworks. This process could be done just as well in Sketchup, Inventor, or Autodesk 123D.
Here is a video of the passive amplifier doing it's thing.
The first step was to make a box that would represent the 'dock' area for the phone to sit. I made a simple box, then added a pocket with a slight angle for the phone to rest against. This pocket was made slightly larger than the phone with a case installed on it.