At this point they should really consider dropping the "suffix" to the iPhone model name. They've kind of dug themselves into a hole, name wise, since this upcoming one will be the 6th version of the model. They could name it 5, which would probably only upset us geeks that actually know how many models there have been. They could name it 6, but then the general population would start wondering where 5 went. They could even just name it 4G and procrastinate solving the problem for another 12-18 months.
Or they could just go the way of a lot of their other products and just advertise it as the new iPhone (like the new MacBook Air, etc).