It's just not thicker, says Apple's Phil Schiller.
Last week Apple finally launched the white iPhone 4. As far as online shipping dates tell Apple made enough white iPhones to go around. The Apple Store shipping dates stayed at 3-5 days in the United States. Before the launch of the white iPhone 4, Apple fans hoped that there will be some kind of improvement or difference in performance. Well, there are differences in the hardware of the white iPhone compared to the black model, but they do not make a difference.
Japanese blog MacOtakara (via AppleInsider) identified in a tear down that the camera sensor and the proximity sensor are slightly different. These differences are though only addressing the different requirements of the white casing.
Another difference raised some eyebrows. The white iPhone is 0.2mm thicker according to measurements from some of the first owners. 0.2mm is really almost nothing, but it got a lot of attention. This attention triggered Apple's Phil Schiller to respond to an inquiring user on Twitter, saying: "It is not thicker, don't believe all the junk that you read." If 0.2mm is making a difference is really up to the observer. I would not care and would never come to the idea to double check it.