I use a griffin hard case that has worked well. However I got a small piece of grit cought under the back and it scratched my phone when I removed it for cleaning :'(
Incase Slider tbh
I don't have an iPhone 3g, but the slider's the best of the many 3g cases I've looked at and played about with. You can get them in Apple Stores![]()
just ordered a SwitchEasy Rebel Case
http://switcheasy.com/products/Rebel/Rebel.html#
some nice reviews on youtube of it.
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Hope this helps