Besides the size of the phone, a teardown of the white model shows that Apple had placed the camera lens further back than where it appears on the black iPhone 4. And while the exact difference isn't known, the white and black iPhone 4 units each have a different proximity sensor. Besides differences in the actual sensor, the white iPhone 4 has an easier to see slit where the sensor resides.
Why the changes? Some of them were probably done in reaction to the leakage in light that was considered to be the main reason for the 10 month delay in launching the product. Other changes were most likely in response to problems that were proprietary to the white color. Apple co-founder Steve Wozniak, who modified his own iPhone 4 to a white version using Foxconn parts purchased online, said photographs using flash came out as if they were, "taken through cellophane."
In Asia, the white Apple iPhone 4 has been a smash hit selling out in Hong Kong in just 1 hour while in mainland China the phone also sold quickly. One analyst expects the white model to sell 1 to 1.5 million units each quarter until the launch of the Apple iPhone 5 which is expected in Q4.