I did some reasonably careful measuring and it looks like a 4" screen is not an option for the iPhone 4/5 if they keep the same housing. 4" just won't fit and there would be no edge for light blocking. The most they could fit in (keeping the same aspect ratio) is 3.7" and that would hardly be worth the bother. They could go to a 16:9 ratio (using the same width as the 3.7" screen) and give us 4". That wouldn't be too bad, but apps that rely on the old ratio would have black bars. Anyway, pic below... What do you think Apple is going to do?