Since Verizon will begin selling the iPhone 4 on Feb 10th, who's planning on switching?
Main differences are that AT&T's version is a true world phone and has simultaneous voice and data. Verizon's is straight up CDMA just like most of their phones. AT&T's data plan is also cheaper as it starts at $15/mo. Their $25 data plan covers almost everyone's usage so unlimited is negated except for a small percentage of users.
There will be a new iPhone in a few months so I think people that jump on it early will have buyer's remorse.