iPhone 5 And its New Screen
The new screen ought to be:
16:9 aspect ratio for watching movies
Continue to support older iOS apps
Maintain Retna Display designation
At the current size, the 3.5 inch screen of the iPhone 4/4S is 329 PPI.
However, Retna Display designation is not a set number, rather it is the relative point by which one cannot differentiate one pixel from another. With a larger screen, one would hold it slightly farther away, so we can allow the PPI to decrease slightly with no ill affects on our designation or apparent screen quality.
All these criteria can be met by simply making the screen no larger than 4.3 inches, and increasing the resolution from 960x640 to 1138x640.
4 inches - 326 PPI
4.1 inches - 318 PPI
4.2 inches - 310 PPI
4.3 inches - 303 PPI
We will have a 16:9 aspect ratio, we will maintain backwards compatability with older iOS apps, and we will maintain our Retna Display designation.