Home-brew, low-tech iPhone amp made of PVC and an old bike horn. Adds a little oomph, without powered amplification. It works well, tho it amplifies some frequencies better than others (like vocals).
The bike horn (with it's noise maker removed) had just the right amount of threading on the end to screw into the soft plastic hole, and be flush with the inside of the PVC. It sits directly in front of the tiny mono speaker. Leaving the ends of the PVC open allows for a more expansive sound and lets more treble escape. The weight of the horn keeps the phone from tipping back.