The iPhone 4/4S screen is 960 x 640 pixels and the concensus is that the iPhone 5 will bump that resolution up to 1136 x 640.
But a case can be made for also extending the short side from 640 to 720 pixels to allow it to display "true HD" content without as much scaling.
DisplayMate Technologies' Dr. Raymond Soneira thinks that a 1280 x 720 "true HD" resolution would be much better because it would reduce processor cycles and thus extend battery life:
That's 176 more vertical pixels, so existing Apps expecting 960x640 will simply be Letterboxed with 88 pixel black borders on the top and bottom. But since we are already Letterboxing, why not raise the 640 pixel base up to 720 pixels and add 40 pixel black borders there as well? Even better... 720 pixels is true HD High Definition - that is not only a major marketing advantage but there is much less processor overhead (and battery power) from rescaling content from 1080p to 720p than to 640p (rescaling by 3/2=1.50 rather than by 1.69).
If the aspect ratio of the iPhone 5 increases from 3:2 to 16:9, it stands to reason that it will maintain the same 640 pixels horizontally and add 176 additional veritcal pixels.
A 640 pixel width also makes more sense from a software perspective because it maintains compatibility with existing apps -- which would only have to letterbox on one axis. Developers who update their apps for the iPhone 5 will only have to add additional pixels on one axis, instead of two, which is exponentially easier.
Soneira also weighs in with his predictions on other specs of the anticipated iPhone 5 display, including PPI (326, but as low as 286), reflectance (under 5 percent), contrast (CRHAL of 90, like the Lumia 900) and color gamut (100 percent of the sRGB) in an excellent post on the DisplayMate website.
Other HD smartphones like the Samsung Galaxy S III and Galaxy Nexus have 1280 x 720 pixel resolution but they're Pentile Matrix Super AMOLED displays which aren't as sharp as true RGB panels. HTC, Samsung and Google will claim that their devices have more resolution but the iPhone 5 will most likely be sharper.
But forget the bogus Pentil displays, the real questions is how the iPhone 5 panel will stack up against the new RGB panels next week's rumored HTC ONE X+ and the 4.7-inch, 720p, Super LCD 2 panel coming in the HTC Zenith.
Is a 1136 x 640 iPhone 5 display going to be competitive with a raft of new Android devices coming to market -- for a whole year? I'm skeptical.