Like I said the VAST majority (85% using your numbers) will be existing VZW customers. A huge chunk of those will be in major cities such as L.A., NYC and S.F.
And I'd be willing to wager that many of those polled who "would" switch, won't now that they have seen they're not saving anything.
Conversely, there will be a certain, albeit it rather small amount of Verizon customers that will be outraged for whatever reason after they've held out this long, and switch to AT&T.
In the end, when all is said and done, around 9 out of 10 V-iPhone buyers will be existing Verizon customers.
There's only ONE reason to switch- if your phone service really sucks. It's definitely NOT about money.