I came across this Acoustic iPhone Amplifier on Pinterest and had to make one. The awesome part is, no power required, just 4 pieces of wood glued together. I was surprised on how well it amplified the sound. I did this all for free, didn't have to but anything. I used materials that I already had in my garage. This would be great to use outside, camping, etc. Also you can adapt this to any phone, just change the measurements for the phone slot to fit your phone.
If I had to make this again, I would find a better way to cut out the three circles. Probably make some short of jig for my router. After I glued the three pieces together, it took a little bit of time to sand and make the circle(speaker) smooth. But in the end, it turned out great. I was very surprised how well it amplified the sound. Pretty amazing what 4 pieces of wood glued can do.