There is no reason to think that Apple would have to stick with AT&T or Verizon. Apple could crank a mixed CDMA and GSM phone. That would free Apple to license chunks of bandwidth from both Verizon and AT&T. If those companies can’t come through with the necessary bandwidth Sprint could always be added to the mix. The names aren’t really important, the important thing is that Apple could buy up the necessary bandwidth to keep users happy. via Why Do iPhone Users Have to Put Up with Carriers? – AppleMatters.
Verizon sold out the iPhone within 17 hours. All those who ordered the Verizon iPhone are most likely people for whom the network mattered.