That makes no sense. Why would they completely skip a number. That would confuse so many people. If anything it will be iPhone 4G or LTE. I still think it will just be called iPhone 5 though. Who knows... guess we'll see.
No one here knows the answer. I could see them calling the iPhone "iPhone 5" to capitalize off of the huge publicity surrounding the iPhone 4S. They might go with 6 for the sixth model. If anyone tells you they know for sure, they are either 1) lying or 2) about to lose their job at Apple