It is extremely unlikely that Apple would leave AT&T. More likely, they would simply add more carriers.If the iPhone doesn't leave ATT, I'm just gonna jailbreak and use my iPhone over 3G for EVERYTHING.
Let's face it: the fact that Verizon CEO Ivan Seidenberg practically begged for the iPhone a month or two ago indicates that they are not getting the iPhone in the near future. Apple's partners generally clam up real quick when there's a deal in the works.
Plus, there is no indication that Apple has been heavily hiring CDMA engineers. The tech media would have reported this if it started happening.
Verizon users aren't getting an iPhone this year.