This is a 3D print I made in my free time (when I should have been doing engineering in class.) It works for all 3 models of phone, and the model comes with the CAD .ipt files for modification. The Amp uses no electronics, and will boost sound by at least 2x.
Step 1: Download Model
File is uploaded on thingiverse here: http://www.thingiverse.com/thing:1467019
If you like it, check out some of my other models.