You've seen the commercials. You've heard the debates. You can't go a week without hearing Verizon Wireless, Cingular, or Sprint claim to have the biggest or fastest wireless network in America... or sometimes all three of them!

So who's right? Who really does have the biggest cellular network in the U.S.? I put the question to the big three networks to find out how they make their claims and what data they had to back it up. (And while I love T-Mobile as much as anyone, its network is decidedly smaller in both coverage and number of subscribers, nor do they make such grandiose claims, so it was originally excluded in this survey (update below).)

For starters, you'll see that no carrier claims to have a larger network based on actual geographic coverage (except Alltel, see below). In fact, no carrier even seems to know how much square mileage its network actually covers. It just isn't measured, and that data doesn't exist.

What cellular carriers use instead is a measurement of the total number of people who are physically located in the service area of the carrier. The total number of people who can reach the network is how carriers make claims about the size of their coverage; presumably the more people you can reach, the more physical ground you cover, but that's not necessarily true.

Obviously, more people live in urban areas than in rural ones, so all carriers focus their efforts on reaching the most people where they live. Rural coverage exists, but there's no way to easily tell whether one farm or another is going to have coverage aside from looking at a coverage map in detail.

With that in mind, here's what the networks said—this is all from their own mouths; I'm not spinning the information at all—about their wireless service (in the order they returned my calls).

Cingular
Cingular's standard GSM voice service reaches 270 million people, and its 2.5G EDGE service (a service that's a bit faster than GSM) reaches 250 million potential people. Cingular's 3G HSDPA service reaches 70 million people in "80 to 90 cities" and covers 40,000 miles of highway. Cingular also points out that its network is all-digital and has no analog roaming, making it the largest all-digital network in the U.S. Since it's GSM, you can also take your phone worldwide (with voice service in 200 countries and data service in 100), which you can't do with CDMA networks like the other two carriers have.

Verizon Wireless
Verizon offers standard voice coverage to 291 million potential people if you include its roaming partners who provide service where Verizon does not. If you discount the roaming partners and just include towers owned and operated by Verizon, coverage is 255 million people. Verizon's 3G EV-DO network reaches 150 million-plus people. Verizon also claims to have the largest network by number of subscribers: 52.6 million retail subscribers and 54.8 million if you include resale/rebranding agreements with other carriers. Verizon also notes that J.D. Power consistently ranks Verizon as having the highest overall call quality on the market, along with T-Mobile. Verizon also claims to have the most reliable network in the States, based on a variety of third-party studies.

Sprint
Sprint's standard voice service reaches more than 295 million people (including U.S.-owned islands like Guam), and the Nextel iDen network reaches 264 million people. Sprint's 3G EV-DO network reaches 158 million people in 220 markets with more than 100,000 residents and 486 airports. Sprint's recent claims are that its broadband service is 5 times faster than Cingular's, but this is comparing to Cingular's old 2.5G EDGE service and not its newer 3G service (which has a comparable speed). Technically speaking, Sprint suprisingly has the largest amount of coverage.

Alltel (updated 10/2/06)
Here's what Alltel (finally) says: Alltel has 11 million customers and cover 72 million potential customers. "Our network covers more square miles nationally than any other carrier's network—hence we are the largest network." When I asked how the Alltel network could be larger geographically but cover less than a third of the population that the other carriers do, Alltel said, "There is no tie between pops [people covered] and network coverage... our build-out network covers more square miles than any other carrier's... pops really pertains to population in a licensed area." It seems to me that there actually is a strong tie between the geographic size of the network and the number of people living inside that area. And since no other network actually even measures the size of its network geographically, I have to take these claims with a grain of salt.

T-Mobile (updated 10/3/06)
T-Mobile got back to me with this information: T-Mobile reaches 275 million people in the U.S. and has 23 million customers. The company didn't offer information about how much of its coverage is through its own network vs. its affiliates.

And that's the scoop!

So who's got the biggest network? If you compare geographic coverage maps, it sure looks like Verizon, but Sprint genuinely seems to cover more people, if by a small margin, with both voice and high-speed data. (Those coverage maps are hardly standardized, so it's tough to draw conclusions based on them.) Cingular, however, does have an advantage by having more digital service. Analog roaming, common in rural areas, can be expensive and buggy, and many phones simply don't have analog radios at all any more. Cingular's international support is also worth noting. Then there's Verizon: Those call quality claims are hard to ignore and are probably more important to most users than a few extra towers out in the boonies.

Bottom line: All three networks are suitably large for more than 99 percent of U.S. users. Unless you frequent parts of Montana near the Canadian border, you shouldn't experience dead zones more than once in a blue moon. My recommendation: Find a phone you love and a plan you can afford and give it a try near where you live, but don't worry too much about who's providing the service.

Note: This does not mean that all three carriers are equally appropriate for every mobile phone user, but that, on average, they all have coverage that spans most of the country. Check out this post for more help on how to choose a cellular carrier.