Verizon screwed themselves a lot earlier than that, IMHO
I was once a faithful Verizon customer, but I dumped them long before the iPhone existed - because their rate plans were terrible.
I know with all of AT&T's issues, it's easy to reach out to any competitor as a "better" choice - but seriously, Verizon would be among my *last* choices, if I could have my pick of any carrier for the iPhone.
For starters, I was really using a lot of peak minutes at one point during my Verizon contract (used the phone all the time for the on-site computer service business I was working for, plus lots of personal calls). My bills started getting ridiculous, due to constant "overages". Verizon, however, refused to sell me a plan with any more peak minutes, claiming I was already on the "largest plan they offered". (Sprint, by comparison, was happy to charge reasonable little $5 fees to buy blocks of extra minutes as you went over their monthly allotment. And if I had used U.S. Cellular, it wouldn't have even become an issue, since all incoming calls are free with them - and that was easily 3/4ths. of the calls I was dealing with.)
Additionally, Verizon is expensive for their data. Unlimited data plans are typically around $49.95 per month. Sure, they could do what AT&T did and make a special set of pricing plans for iPhones -- but my guess is that if they did, you'd be paying at least $10-20 more per month than AT&T's rates.
Lastly, while I didn't have all the dropped calls I get with AT&T, I did experience a lot of noisy calls I had to cancel and re-try to get a usable connection. Verizon was really bad about giving me a call where I'd hear another conversation going on in the background, or my own voice echoing in the background every time I spoke.
Verizon dumps a LOAD of money on advertising, but just because we all know the face of the "Can you hear me now?" guy doesn't mean they *really* have the most trouble-free and reliable network in the marketplace. My experience is, they have an "adequate" network with "above average" coverage, but you pay top dollar for something that's not really "impressive" at all on overall call quality.
Ya. I say BLA BLA BLA Verizon. It won't happen till 4G, and who cares!

Verizon had the chance and screwed themselves over, so they can eat it!