Urikane, an iPhone user with a LOT of time on his hands, has put together a (nearly) full alphabet using 540 apps. Each screen contains one letter -- except for the W, which as our commenters point out, was skipped. It would be especially hard to do on a 4x4 matrix, unless one could find app icons with the right contours to simulate the angled sections.
Outside of this being really clever, you have to admire the resolve of Urikane to actually get this done. It must have taken forever.