Based on the photos below, the new white iPhone 4 is “fatter”‘ than it’s black counterpart. Not much of a difference, but enough to cause problems with cases fitting onto them.
Based on these photos, one could assume the new white iPhone is thicker because of the thicker plastic needed for the white model. Because of the white color, Apple needed to filter light better on the phones exterior, thus creating a thicker case. I’m guessing with a bit of tweaking, the iPhone 4 cases will fit fine. However, several people are stating that the hard plastic cases are having trouble fitting, but the jelly ones will work fine. There are no technical differences listed by Apple between the 2 models, so it could be an unknown issue to Apple from manufacturing. In any case, it will be interesting to hear what Apple has to say regarding this issue.