Last february, Macrumors published the back side of what was reported as the enclosure of the future iPhone 3GS.
With the recently unveiled model, we now know that it was not a fake:
If one look close enough, you will see that the FCC information and numbers fit. So, the photo published by Macrumors was most likely a prototype that did not make it. But having the FCC information already engraved on the enclosure indicates that this rough black design was dropped late in the development roadmap.