It looks like there is another difference. The white iPhone 4 is also slightly thicker than the black iPhone 4.
MacRumors reports that one of their readers noticed it when the white iPhone 4 didn’t fit in his Incase slider case.
Just picked up the white iPhone 4 and realized it doesn’t fit into my Incase slider case. It appears that Apple has increased the size of the plastic that borders the glass on both sides by about 1mm.
Ryan Cash of MarketCircle also noticed the slight difference in thickness:
A colleague of mine just picked up a 16 GB iPhone 4 in white. I was a bit surprised when I picked it up off his desk (I had my black 32 GB in my other hand at the same time) – it immediately felt thicker.
You can checkout the images below, which shows that the white iPhone 4 is slightly thicker than the black one: