A 4-inch iPhone screen →

Pretty interesting. The above clip is from the most recent Vergecast in which a caller named Colin describes how a 4-inch screen could fit on a device that's about the same size as the current iPhone: by making it taller rather than wider. Ignore Josh Topolsky's insistence that Colin is describing a 4.6" screen with a virtual Home button: I don't know where he got that. Paul Miller (on the right) seemed to understand Colin more clearly. (I seriously doubt there'd be a virtual Home button)

A user named modilwar later expanded on Colin's idea in a Verge forum thread.

That thread got pretty popular and when John Gruber of Daring Fireball noticed it he had only this to say:

Methinks “Colin” wasn’t merely guessing or idly speculating.

A peculiar response. Like Macrumors noted:

Gruber has been known to speak coyly about his occasional inside knowledge, it is unclear whether he has independent knowledge supporting the idea of a taller display for the iPhone or if he simply has a gut feeling that "Colin" may legitimately be tipping some information at least partially tied to Apple's thinking.

This is probably the largest amount of discussion we've had about a bigger iPhone screen, and modilwar's post brings up some good points, but of course there's some skepticism to be had here. Looking at iPhone mock-ups made by commenters in modilwar's post, the Home button and speaker seem to be pretty darn cramped, and a 6-row Home screen looks a bit odd as well. As he notes, games wouldn't scale to the new size as nicely either, so there would definitely be some growing pains to be felt if Apple were to make such a switch.

Still, Gruber's coyness over his typical "3.5 is perfect for one-handed operation"-type rejection is pretty notable, so modilwar has something here worth thinking about.