Apple has 89 million reasons to consider Verizon in the US, and nearly 500 million reasons worldwide to consider a 3G CDMA iPhone. As I've said before, I've got to believe that Apple would love to sell me a CDMA iPhone next year and then another LTE iPhone two years down the road.
I have only heard one valid reason not to -- if the two cannot agree on revenue sharing. To say the technology is not there, or would be too expensive, or too complicated to support, is all FUD. Period.
If Verizon can sell enough Android or RIM smartphones, at some point they may not care to give up data revenues to Apple just to have the iPhone.
In the past, Apple has had the mindset of "we build what we think is best, and let people come to us, and to heck with the rest". But recent developments (Intel chips, app store, DRM-free music, etc) seem to indicate that Apple is willing to reconsider some of its perfect ideals if it can drive sales without compromising the overall experience. Let's be honest, Steve isn't going to live forever, so I think he's finally realized that he need to get busy on that world domination thingy.
For many of us, AT&T's weaknesses far outweigh its strengths to the point where changing carriers just to get a phone is not an option. Network issues aside, Verizon's free "in network calling" far outweighs rollover minutes for me.
I've had no issues with Verizon's network (despite having a smartphone and two data cards), and most of my family and friends are on Verizon, so I rarely use peak minutes. I have two friends on AT&T, both switched from Verizon to get the iPhone, and would switch back in a heartbeat because their friends and family are mostly on Verizon.
Let's face it -- two year contracts have long expired, and those who are willing to switch carriers to get the iPhone have long since done so. Many of the rest of us are willing to wait for a Verizon iPhone, and will make do with a iPod Touch if that never happens. Plus there are millions of people who would never consider the iPhone, but would probably buy it if they walked into a Verizon to get their new phone every two years and saw it in action (yes, I'm saying it is that good).
Apple may not be crazy about building a CDMA iPhone, but they would certainly be fools not to consider it.