Take a broken iPhone 4 to get it fixed and come out with a 4s in its place.

According to Gizmodo, Apple had supply constraints on the black 16 and 32 gig iPhone 4 (gsm model.) So Apple has told the apple stores to replace with the black 16 gig iPhone 4s model. I have a feeling that this will not last long as Apple has already fixed the supply issues with the white version and I'm sure the black ones will be back in the supply chain fairly quickly.