T-Mobile has the best plans with the lowest per minute rates (in most
cases), unless of course you really can benefit from the rollover
offerings of Cingular.  I am a former Cingular customer who has been
with TMobile for some time now.  No complaints (unless you count the
fact that TMobile may not have as good a selection of higher quality
phones... eg. Cingular has Moto V551, TMobile is still fussing around
with a comparable V330 that was supposed to be released last month), and
where I am in Northern California I have better reception at my home
with TMobile than with Cingular.... don't ask me how since they are
supposed to use the same network, but in my town it looks like TMobile
has their own towers.... You can check TMobiles site for towers (but I
don't believe it includes the 'shared' towers it has with Cingular:

http://www.t-mobiletowers.com/homeTowers.aspx

Best bet is to actually TRY the coverage at you house and business...
there is NO BETTER WAY to compare...

Good Luck,

SFB

Well it's guaranteed your coverage will improve at least 1000% no matter
what you switch to.  Can't comment on T-mobile.  I switched from Verizon
(good coverage) to Cingular (better coverage, a lot cheaper too) because
Verizon's admitted billing errors were driving me up the wall.  I've been
with Cingular a couple of years and the only billing error I've seen was
right when we moved.  But it was corrected quickly at least.  -Dave