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Schematic of the rumored next generation iPhone with a 4-inch screen appears to have been leaked to various blogs like iLab and Cydia Blog. The schematic shows measurements of various components found on the iPhone's front panel including the the widely rumored larger display.
The "active area mask," or the portion which houses the display, measures 3.55 inches vertically and 2.02 inches horizontally, according to the schematic.