Sorry, I should have narrowed that down to larger-screen
devices. You know, reaching 440 ppi on a small-screen device such as a smartphone isn't quite the same achievement (although definitely admirable) as to do it on an 8-inch screen. You can also observe that trend on Retina-screen MacBooks, in that their screens don't approach the quality of the iPad (let alone iPhone) Retina screens ("only" 220/227 ppi on the MacBooks).
By the way, can you give me the exact calculation for that hypothetical new iPad mini with a Retina screen (doubling the current resolution)? I'm too inept or lazy to calculate it myself.
iPad 3+ currently has 264 ppi, and the iPhone 4+ is at 326 ppi. The current iPad mini is at a paltry 163 ppi, almost as bad as the original iPad (132 ppi). If anyone can give us the exact figure for iPad mini with Retina, please do.