Since the first, Apple is very good in terms of keeping their secrets about upcoming Apple devices. Therefore, design of the next iPhone is still a mystery to date. May be the iPhone 6 will use a bendable display with a resolution of 1615 x 800 pixels, HD front-facing camera for Face Time, Near Field Communicator, and lighting connector. 3D video render and some other features such as multi-touch gesture with virtual control button may be available too on the next iPhone.
The video below is about iPhone 6 concept by a designer named Raphael.