This cool little silicone Horn Speaker uses no external power to amplify your iPhone 4's speaker passively, like an old record player. The iPhone 4 Horn Stand can boost your speaker by 13 decibels while holding your iPhone vertically or horizontally.
"So it basically turns your flash phone into an i-phonograph! You can also still charge your phone whilst the horn speaker is attached.The Horn Stand makes a fabulous novelty gift for iPhone 4 owners, especially if you’re looking for iPhone gadgets that have both that "cool and cute" factor!"
Yours for about $24 here.