Case manufacturers are a great source of leaks about a future product's design. Without showing case makers the device early, a new product won't have the full line of accessories for it.
For one reason or another, people love to encase their smartphones in cases; and if the iPhone 4 is any indication of Apple's design direction, the next iPhone will likely find homes in many different cases.
A leaked case design out of China, as shown by Gadgets DNA, suggests that the next iPhone will have a bigger edge-to-edge screen design that could means a bigger LCD in the current iPhone 4's form factor.
Another new design feature is a second cut out hole on the back. Some believe it to be a relocation of the camera LED flash in an effort to improve low-light performance.