Just checked out this cool polished aluminum speaker from sony, It greatly improves the speaker on the Iphone and looks awesome. It would be a great speaker for a public pool or other event. I was testing mine out while spring cleaning at the garage and it was loud enough for my neighbors to hear. It not only works for the Iphone but many devices that use a standard 3.5mm jack. Uses 3 AAA batteries and can run up to 10 hours. Buy it here

Works for these phones & many sony phones also
Apple iPhone, iPhone 3GS, iPhone 4
Blackberry 8110 Pearl, 8300, 8520 Curve, 8900 Curve, 9000 Bold, 9105 Pearl 3G,9300 Curve 3G, 9500 Storm, 9520 Strom 2, 9700 Bold, 9800 Torch
Dell Streak
Nokia 2730, 5230, 5310, 5800, 6303, 7230, C3, C5, C6, E5, E52, E63, E72, N76, N78, N8, N81, N82, N95, N96, N97, N97 Mini, N900, X2, X6
Samsung B3210 CorbyTXT, B5310 Corby PRO, F490 Tocco, Galaxy Tab, i5510 Galaxy 551, i9000 Galaxy S,S5620 Monte, M7500 Armani, S8500 Wave, Wave 723
Vodafone 360 H1, 543, 845
HP IPAQ 214
HTC Desire, Desire Z, HD2, HD Mini, Nexus One, Tattoo, Wildfire
LG GT350, GT540 Optimus, KM900 Arena, Optimus 7
Motorola E8 ROKR

Sony Ericsson provided us one of these free of charge to check out