We have AT&T, but we live in PA, so our coverage here will be different. We usually get pretty good reception whereever we go. When we vacationed in NH two years ago, I really do not remember having trouble getting reception. I specifically remember having coverage at the summit of Mt. Washington because my daughter was on the phone with her friend who was on the 90+ degree beach! However, just last weekend, we had little or no reception at the campground we were visiting. My daughter did get one bar in her bed, but my hubby and I got nothing. He and I have the same phone, a Sony Ericson. She has a Motorola Razor. I have had several different phones, and I think the phone you choose also has a lot to do with reception.
Maybe you could include a section in the campground reviews for cell coverage? Just a thought.