I've completed the parts and photography for Paper Horn project. I've made a version that works for Galaxy S2 and S4 and one that works for iPhone 4S, these are the phones that I have access to in our house. It should be fairly easy to adapt it for use with other phones. It'll be up in the next 24-48 hours.
Did you see this in the comments?
Simon68 sent in this fantastic picture of the paper horn he modified with alphabetti spaghetti and copper coloured paint. Isn't it awesome!