VZW has brought out their version of popular GSM phones before. What you get is a watered down, restricted version of the original. My first experience with that was when the Moto Razr came out. I still use my 1st gen razr for cheap international roaming. The one my wife got through VZW is about a notch up from a furniture store prop. At least with the VZW iPhone, that will mean no international roaming (ala Blackberry 8830 - despite it's disabled gps feature intended to "force" you to buy the VZW add-on), unlocking it will be difficult and ultimately pointless, and no simultaneous voice and data.
The WSJ reported that one major reason Apple did not partner with VZW on the iPhone in the beginning boiled down to control over applications. As far as I can tell, VZW is still wrapped around the axle of trying to profit off of proprietary content that is widely available and free elsewhere (if your phone supports it). Their voice and data networks simply rock, but their cobbled up, proprietary phone choices keep me away. Apple and AT&T aren't exactly known for their openness, but at least you get the full feature set.
As far as 3G 4G or 12G, who really cares anymore? None of the providers really can or are willing to deliver anything close to theoretical speeds. When they finally do upgrade, it takes them another year to refresh their phone offerings to really take advantage of any increase. Just take the marketing fluff, multiply by 0.2, and that's what you can expect.