People in this thread need to realize two things:
1. If the iPhone goes to Verizon, Apple would never allow Verizon to add any extra crap to it like they do with other phones so don't start harping about how Verizon would be horrible for the iPhone...If Verizon wanted that, we will never see the iPhone on Verizon.
2. Apple will not deal with CDMA so don't say that's a reason for the iPhone not going on Verizon. LTE is coming for both Verizon and AT&T. Apple is most likely already in talks to get LTE working in the iPhone and so Verizon could very easily have the iPhone in 2010 or so when LTE starts going up...but maybe more likely in 2011.
Now on to speculation: Since Verizon will have LTE before AT&T there's no doubt AT&T will try and lengthen this exclusivity. At the same time, Verizon would probably love to have the iPhone on Verizon LTE for a year while AT&T is still on 3G. I personally hope, and speculate, that Apple will want to upgrade the iPhone to LTE as soon as possible...thus, an exclusivity deal into 2011 may not be the right move. At the same time, it's possible that they continue with AT&T until both AT&T and Verizon have LTE and then upgrade and extend across all companies with LTE...