As Verizon Says: It’s The Network
The main reason to have a mobile phone is that it works where you are. If it doesn’t work where you are, what’s the point of having a mobile phone? Of course no carrier has perfect coverage everywhere, but it should work a good portion of the time in a good portion of the locations you are at on a regular basis. Why people don’t buy service this way is beyond me. Oh yeah, it’s because situation change, but the carriers insist on locking people into two year agreements with stiff early termination fees. So a service that worked great for you one place, but not so great another place.
Let me offer a personal example. When I lived on the other side of town, AT&T Wireless (now Cingular) had non-existant coverage–it’s only marginally improved if I recall correctly. On the other hand, VoiceStream (now T-Mobile) had fantastic coverage. In fact, I could see the tower from my apartment balcony. 
Where I live now, neither carrier has great coverage, but Cingular definitely has a leg-up over T-Mobile. I can use my phone inside my house most of the time and not lose calls with Cingular. With T-Mobile, it’s a bit more of a crapshoot outside of the confines of my upstairs office.
(I have no idea how Sprint or Verizon did at either place. I use the only proper worldwide standard GSM, not this CDMA stuff that Qualcomm came up with and charges people who don’t use their chipsets more for royalties on CDMA, but I digress.)
One thing I like about T-Mobile is that they actually post street-level coverage maps right on their site. You can type in any address and it will give you a rough idea of whether or not you will be able to use your phone there or not. The maps err on the conservative side for sure as my house is technically in a no-coverage zone, yet I still get signal and can usually make a call up in my office or outside. It also tells you if the coverage is GSM 850 or not, which is important since T-Mobile only began selling GSM 850 phones recently.
To my knowledge, no other US carrier gives the kind of detailed information about coverage that T-Mobile does. It seems weird that the two companies that make the biggest deal about their network, i.e Cingular and Verizon, do not provide anywhere near this level of detail on their web site. It is possible to get a bit more details from Cingular, but you either need to call Customer Care or go into a corporate store to get them to show you the information. I shouldn’t have to, I should be able to look it up from my house and compare.
If T-Mobile could somehow figure out how to get better signal at my house, I would use them exclusively, even if they are behind the times with data services.
