It definitely will not be the iPhone 4G. Neither ATT nor Verizon are in the process of deploying networks that the ITU would define as '4G', despite what their marketing crap wants you to believe.
Apple, as we know well, does not capitulate to the network operators like every other manufacturer. Their phone is simply called the 'iPhone'; the name doesn't change per operator for the same device (a practice I've always found surreal). Given this, and the fact that they must satisfy international markets with a single build of the phone (CDMA version aside), many of whom have only just auctioned off spectrum for 4G connectivity, there is absolutely zero chance of Apple introducing a phone with so-called '4G' connectivity or naming a phone as such until it starts to make its presence felt across the world.