There was a recent thread about which cell phone network is best for poor reception areas and I thought I'd relate a personal experience about a different answer to this problem. Last fall
my wife and I met my son and his fiancee at Big Bend National Park for a long weekend. We stayed at the Chisos Basin lodge and had no cell phone coverage. My son makes several trips a year to BB and was our guide. He had us drive over the ridge by the Lost Mine Trail, park the car, and attached a Wilson Electronics amplifier and antenna to one of our cell phones, and voila; we had coverage.
I don't know if the amplifier and antenna will work for everyone; but, it sure did for us.