Amid rumors of a significantly larger "iPhone Math", Instapaper developer Marco Arment has spent time developing some speculation and a few mockups showing how Apple could achieve an iPhone with a nearly 5-inch without disrupting the existing app ecosystem.
The recently rumored, larger-screened “iPhone Math”, or more likely “iPhone Plus”, is plausible as an additional model (not a replacement) alongside the 4” iPhone. And there’s a good chance that it would have a 4.94”, 16:9 screen.
The theory is easy to understand: perform John Gruber’s Mini-predicting math backwards. The iPad Mini uses iPhone 3GS-density screens at iPad resolution. What if an iPhone Plus used Retina iPad screens with iPhone 5 resolution, keeping the rest of the design sized like an iPhone 5?
Left to right: iPhone 5, "iPhone Plus", iPad mini, iPad
In the scenario put forth by Arment, an 1136x640 screen matching the iPhone 5's resolution but blown up to the Retina iPad's 264 pixels-per-inch resolution would measure 4.94 inches diagonally. He notes that maintaining the resolution of the iPhone 5 would mean that developers would not have to make any changes to their apps to support the new device, with touch targets and other elements simply increasing in physical size. While the "iPhone Plus" would not be able to display more pixels than the iPhone 5, Android devices have demonstrated that larger screens are popular with consumers.
As much as we make fun of the Galaxy Note, it sells surprisingly well, especially outside of the United States. Other large Android phones sell very well almost everywhere.
The iPhone has lost a significant number of sales by buyers either wanting a larger screen or being drawn to how much better the large screens look in stores.
Left to right: iPhone 5, Galaxy S III, "iPhone Plus", Galaxy Note II
Arment notes that such an iPhone Plus maintaining the same relative proportions as the iPhone 5 but with the larger screen would measure somewhere between the Galaxy S III and the Galaxy Note II, but that Apple would likely be able to trim down the chin and forehead of the device somewhat to bring the device closer to the Galaxy S III's overall size.
At an iPad-like pixel density of 264 ppi, Apple could have a hard time positioning the iPhone Plus as a Retina device given that a phone is assumed to be held closer to the eye than a tablet, but some consumers may still prefer the option of having a larger screen to offer more flexibility such as being able to zoom out further on text or view small text with the device held further from the eye.