iOS 6 now is able to scale to show five full lines of apps when displayed at a 640×1136 resolution. This indicates that the upcoming iPhone 5 will have a 4-inch screen. The current version of iOS 5.1 can only show four apps when running the same iOS simulator app. There would not really be a need to support an additional row unless the screen was going to get bigger. We’ll find out officially in September though.