The problem is, as an AT&T customer (a company I loathe BTW... in another tab I'm about to pay a $450 bill from them) I cannot use a Verizon tower. (There has been limited benefit to pursuing both the CDMA and GSM technology paths towards a wireless broadband network.) I assume I can't use a T-mobile tower either (there ought to be a Coase equilibrium between GSM carriers, but it would involve billing costs that a true merger could avoid). Thus, I have to pay AT&T, and you T-mobile, for coverage in the same area.

Now, coverage in some highly-populated areas is bandwidth-limited. In other words, there are often enough customers of each carrier in a place to saturate the corresponding antennas. But any time the T-mobile antenna is not saturated and the AT&T antenna is over capacity, there is waste. This waste shows up on both our bills (forgive me for assuming you're a T-mobile customer for the sake of argument).

Obviously, competition is a good thing, but its benefits are easily overwhelmed by infrastructure costs. Electric utilities generally operate very efficiently with government-sanctioned monopolies (and subsidies). The trading requirements enacted in the late '90s to promote "competition" on the grid are widely considered to have failed to improve utility service, and are implicated in things like the 2001 California energy crisis. Since colonial times, the Crown granted molopolies for expensive things like colonizing India...

You're completely ignoring that in many rural areas, there are only one or two providers. When I visit my parents in rural northeast Ohio, there are only AT&T and Alltel (now Verizon) towers. My T-mobile phone roams (free to me) on the AT&T towers and works just fine. The companies can work out roam-exchange agreements among themselves that allow for sharing of infrastructure.