A company called XSKN has revealed a case design described as an "iPhone 3G" case. The 3G version of the case is shown here, followed by the Original iPhone case:
3G iPhone Case
Original iPhone Case
The differences are slight, but correspond to the leaked specs given to case manufacturers. It also appears to be slightly thicker which was also previously claimed. The image of the iPhone itself appears to be a stock photo of the original iPhone, so no conclusions can be drawn from the icons and interface seen.