The new 16:9 aspect ratio will display existing iPhone apps in their current resolution, with black bars either beside the app, if the iPhone is held in landscape fashion, or at the top and bottom if held in portrait fashion. "All your software works just like before," Schiller said.

"Developers don't have to change their apps," said Milanesi. "They will, of course, take advantage [of the larger screen] when they create their next versions. But you can buy an iPhone 5 today and not feel all of a sudden that thousands of apps are suddenly not relevant."

Apple used that same strategy in 2010 when it launched its first iPad, making it possible to run iPhone apps on the new, larger-screen tablet.

Inside, the iPhone 5 relies on an Apple-designed A6 chip that Schiller said was approximately twice as fast as the A4 in last year's model. Apple revealed no details about the A6, however, such as its clock speed and the number of cores it contains.

The iPhone 5 also supports the faster LTE data networks operated by some carriers worldwide. In the U.S., Verizon has the largest LTE network. "It just screams," Schiller said.