Allowing both CDMA and GSM in North America is like allowing left and right hand drive cars simultaneously. Alec nails it. Personally, I'm ignoring CDMA (since I don't have the cash to have a boring CDMA handset, the GSM ones are so much more fun for multimedia creators like myself; I am tempted by EV-DO but again no extra money for this) ; it'll either go extinct or more likely through software all phones will run every possible standard because we are unfortunately not smart enough as a society to just choose one.
The wireless infrastructure is also a commodity. The Europeans got it right when they recognized this and mandated GSM over CDMA. One or the other didn't really matter, by the way. There are technical differences between GSM and CDMA, but at the end of the day nobody except industry people and operators care. What was important was standardization because it allows the ecosystem around the rest of the technology stack to flourish. By choosing not to choose, however, regulators have allowed an artificial lock-in to occur built around networking technologies. The absurdity of the latest round of telephones with CDMA built in for North America, and GSM for the rest of the world illustrates this problem very neatly. Two standards, two sets of royalties, and lord knows how many radios results in a limited choice of handsets, and more expense for the consumer. It's as if we allowed right-hand and left-hand drive cars in North America, built separate highways for each and invited the road operators and auto manufacturers to compete. Then, because some people's houses and businesses are on one road/auto standard and others on another, the industry decided to build cars with two steering wheels that can drive on either road standard.
Consumers are best served when commodities are delivered in standard ways. And because monopolies tend to act in the best interests of shareholders rather than consumers I would argue, in disagreement with my friend Mark, that when the market reaches a point where competition is not being served, standards should be dictated.