Have a look at the Mophie Juice Packs
. It has the rounded back side giving an iPhone 4 a more or less 3G look, and as an added benefit they are add on batteries giving you longer battery life. I may pick up a Juice Pack Air my self, pretty cool looking mix between a 4G and a 3G look.
64GB iPad 3, 32GB iPhone 4, 1G 16GB touch, 4G & 6G Silver 16GB nano, 5G 60GB iPod, 1G AppleTV, 2G ATV, 2.5GHz 17" MacBook Pro