Apple is working on an improved version of iPhone 4, which has an identical form factor. The device will be branded iPhone 4S, similar to iPhone 3GS.
Apple may come out with an updated version of the iPhone 4 in June this year, which could have a SIM-less design and 8 megapixel camera.
Japanese Mac focused blog MacOtakara, cited one of its sources as saying that Apple is working on the improved version of iPhone 4, which has the same form factor, and that it will be branded iPhone 4S, just like iPhone 3GS.
