Matt Yglesias offers part of the answer:
One major impediment to better wireless service — be it for cell phones or broadband internet — is that right now we have television broadcasters squatting on two different swathes of the radio spectrum. One is used for digital television broadcasts and one for analog broadcasts. This came about as part of an ill-advised congressional giveaway in the mid-1990s. The good news is that half of that spectrum is scheduled to revert back to the federal government which will then auction some of it off and let the rest operate as "unlicensed" spectrum, like the spectrum block that current WiFi application sit on.
The bad news is that if you do that, the approximately 13 percent of households that currently rely on over-the-air (OTA) analog television suddenly can’t get any channels. That’s not going to sit well with the voters. So there’s an impulse in congress to push the transition date backwards and hope more people switch to cable, satellite, or HDTV by then. The problem here is that the spectrum in question would be really, really useful to wireless providers and would let them build various cool and awesome things for people to buy. Even better, the spectrum is so useful that the government will be able to get a lot of money auctioning it off. Way more than enough money, in fact, to give OTA households free conversion boxes to ensure that their TVs still work and still have money left over for something else. For reasons that aren’t clear to me, however, congressional Republicans don’t seem to like this idea and are therefore delaying the advent of better wireless.
As long as we are complaining, most other countries are on a compatible (GSM) system for international cell phones but the U.S. is not (addendum: Many of you have written to note that Cingular is one exception to this claim). I can buy a cell phone and sim card in Dubai and use it in Australia or New Zealand but not in Peoria.