Just as we expected, the connector for the camera on the iPhone 4S is different than the connector on the iPhone 4 (CDMA and GSM). This means that you cannot "upgrade" your camera in your iPhone 4 (or downgrade your 4S if for some odd reason you can't handle the 8 megapixel camera). The iPhone 4S connector has more pins. Even if it did fit, I don't think it would work anyways.
iPhone 4 (CDMA and GSM Side-By-Side):