Two iPhones are reportedly currently in testing over at Apple - codenamed N41AP (or 5,1) and N42AP (5,2). They are enclosed in generic cases to hide the design and offer larger displays with a higher resolution. The exact specs of the new display are 3.95" diagonal and 640 x 1136 pixel resolution. Those numbers suggest a pixel density of around 330 ppi, which is nearly identical to the 329 ppi on the iPhone 4 and 4S, so the "Retina" moniker will remain intact.
GSM Arena, iPhone with 3.9-inch 640 x 1136 pixel display in testing
