Why do we care what the market share is for specific transmission technologies? The overall wireless market is extremely competitive.
Very, very few handsets are built for both GSM and CDMA, which is a situation that won't change for quite a while (upcoming next-gen LTE handsets should work on all carriers, but we will see about that).
At the time of the iPhone deal, T-Mobile and AT&T were Apple's only two real options for deployment (Verizon was a negotiating tactic) -- they wanted to build a GSM handset they could deploy globally. The situation would not be any different today. AT&T only won that war because of their dominant position, which allowed them to throw billions at promotions and guarantees -- which, of course, only further worsened T-Mobile's ability to compete (imagine if they had gotten the iPhone instead).
In today's world, if you were Apple, AT&T would once again be able to sit back and dictate terms, as they will be the only real nationwide GSM network in town. It's 1998 all over again, and I don't like it one bit. The other players -- MetroPCS, etc -- are clearly regional / metropolitan plays and do not offer the footprint necessary for an iPhone type device.
As an aside, I would appreciate if your responses were more than one liners.
Nationwide wireless networks are extraordinarily capital-intensive. Absent a massive technological shift --- which may be coming and which AT&T and Verizon are powerless to stop --- there are always going to be a (1) few (2) very large companies providing cell coverage. It may be more expensive to launch a nationwide wireless network than it is to launch an airline.
Meta, responding to your aside: respectfully, no. I'm trying to avoid typing for the sake of typing. I asked a serious question; you answered it; I responded to it with my take. That's how the system should work.
What are you thinking of?
The thing that makes the "OMG $0.20 SMS PAY TO TETHER WTF" people isn't going to be a better cell carrier; it's going to be something that obsoletes cell carriers. Look at the RIDICULOUS PHONE you have in your pocket right now; nothing like it even existed in 2005.
My Dell Axim had a 624 MHz CPU, 256 MB, wifi, Bluetooth, 3,7 inch VGA screen, TV-out and two card slots, one that could be used to upgrade it. 2005.
(Wait a minute; I don't appear to be paying $0.20 for text messages either, and I'm AT&T.)