California, Utah, Montana, Idaho, Nebraska, Oklahoma, West Virginia, Pennyslvania, New York, Massachusetts, Maryland, North Carolina, South Carolina, Georgia, Florida, New Hampshire, Vermont, New Mexico, Arizona, Ohio, Illinois, Indiana are some of the states that I can think of that I didn't have any major issues with my carrier, Verizon (yes, there were some spots in some states that I couldn't get coverage).
Although Verizon may not have the best reception in an area that is "dictated" by a local carrier (like cingular), I have found that in most instances, if I have coverage, there is a possibility that someone I'm with that has another carrier doe not. I have never been in an area where I've not had coverage and someone else around me does.
Tried Nextel, the two way radio is great, however, found that carrier to be the least dependable out of all that I've tried.
I average about 4,000 minutes a month, and although I may not have the "best" plan out there, no complaints so far.
I have heard although, that Verizon via landline is one of thee worst carriers to use.