Rumorsarecirculating that Apple's next-generation iPhone will see the current 3.5-inch screen replaced with a 4.65-inch, putting it on par with the Samsung Galaxy Nexus.
I find this move unlikely for a number of reasons.
First, scaling up the current iPhone 4S 960×640 Retina display screen from 3.5-inch to 4.65-inch while keeping the same resolution would mean that the pixels per inch number would fall from 326ppi for the iPhone 4S to something in the region of 250ppi for a 4.65-inch screen.
That would be a huge drop in pixel density. It's unlikely that Apple would bump up the screen resolution to accommodate for the larger screen because this would introduce a whole host of scaling problems for existing apps.
Doubling the resolution of the iPhone's screen to 1920x1280 would make scaling easier. It's what Apple did when it went up to Retina display on both the iPhone and iPad. But it's highly unlikely that Apple could pull this sort of density off for the next incarnation of the iPhone. A screen like that would have a pixel density in the region of 500ppi, which would be incredibly dense.
Apple might be able to bump the screen size up a big - say to 3.75-inch or 4-inch in size - and stick with the current resolution, but both would mean a drop in pixel density compared to the iPhone 4S. Having said that, at around 300ppi and 280ppi respectively, the screen would have a higher density than the new iPad.
There's another killer reason why Apple doesn't need to mess with the iPhone's screen in that the device is selling phenomenally well with the current screen size. If people wanted a smartphone with a jumbo screen, they'd be buying them in preference to the iPhone. They're not. There's a valuable lesson contained in that observation.