According to the Wall Street Journal, Apple has already started manufacturing the next iPhone, dubbed the 5S, so that it can be ready for a summer release. From what we know so far, the device will look similar (if not identical) to the iPhone 5. This is a common practice for Apple, which tends to redesign devices with “full” generations (i.e. the iPhone 4, the iPhone 5) and stick with the same design for the “S” generations (i.e. the iPhone 3GS and the iPhone 4S).
This release will likely be focused on an internal boost such as boosting the processor. The iPhone 4S was the first iPhone with a dual-core processor, so maybe the 5S will be the first with a quad-core processor? The iPhone 5S might also offer some new features; the iPhone 4S was the first iPhone with Siri and the iPhone 3GS had video recording and a compass. According to John Gruber (a well-known Apple blogger), iOS 7 is “running behind,” with Apple getting engineers from OS X 10.9 to start working on iOS instead. This update will be overseen by Jonathan Ive, which might mean we’ll see an interesting new minimalistic design. iOS hasn’t changed much visually since release, so a design overhaul would be nice to see.