I'm not a Verizon basher, and it's fine with me if Apple makes an iphone for thier network. Actually I would most likely welcome the move since it might bring better rates for me with the increased competition. But I would not drop At&t for Verizon for several reasons:
1- I've had no problems with At&t and the coverage in my area is excellent.
2- With Verizons network you can't talk and access the data network at the same time, which some might think is cliche, but I've use this feature quite a few times. Why on earth would I give up functionality?
3 - The Verizon iPhone, if only CDMA, would be neutered since it would most likely be good on only Verizons network. (No international capabilities.)
(1) That's good for you, and unless you are dissappointed with ATT, there is no reason to switch....
(2) As many previous posters have noted: us CDMA users are used to this. It's only occasionally a impediment. Maybe it will be a bigger impediment once we have Mobile Safari, and web surfing is something that you do regularly on your phone (I do regularly surf on my 8330, but it's limited, for sure). But right now, I'd be happy to be able to surf at any other time on Mobile Safari, than when taking a call, rather than none at all.
(3) I don't think this will be the limitation you believe it is. On average, a lot Americans rarely leave the country. Many can indicate possible well intentioned reasons, others can mention false intellectual superiority reasons: but for me, I like our culture, and other than wanting to driver Nürburgring in a Mustang 5.0L or a Camaro SS 6.2L, or a Corvette ZR1 with the blower, I have so little interest in leaving my country. Plus, as I understand it from people who *have* left the country with their iPhones, it's a real pain in the pocket book. I hear that most businesses just rent you a new phone when you get there. I suspect if you are rich enough to afford roaming in Europe on your USA iphone, you can probably afford to just buy another one pretty easily for a trip "over there".
CDMA just does so much better with less towers, and its why ATT doesn't have even simple voice coverage in rural areas. Farmers could be a big user of the iPhone (I could think of a bunch of killer apps for farming of any sort), but there just aren't going to be a lot of rural areas with even Voice or Edge coverage, much less 3G from ATT. Verizon on the other hand, because of a lower cost of entry to a given market because of their wireless technology, has coverage in most of these areas, either by roaming agreements with smaller providers who own local towers, or by direct tower presence.
GSM, from the git-go was a metro-area digital technology, and it has cost ATT in the US. I suspect they are merely "hanging on" to their current network with the lowest cost upgrades, until LTE is big time. Then they can roam on Verizon networks (if deals can be struck --- that will an interesting story to watch).
LTE was not designed as a voice substitute, but mostly for broadband. The first LTE devices deployed in the USA will be laptop dongles and cards for other things with large batteries.