Lassig,
The cornfield I live in also has horrible cell reception. I found a company called Cellular Solutions and their suggestions for me wroked as described. I bought an external receiver that I have mounted on a pole about 18' above the ground on the corner of my shop, a decent sized amplifier, and splitter, and a couple of internal antennae. I have a 50x100 insulated metal shop that is also skinned with metal on the inside and a 16x16 office on one end. My amplifier feeds an antenna both in my office and in my shop. I bought a dual band amplifier. No matter who walks into my building (cell phone carrier)the signal strength lights up light a Christmas tree. It was an excellent purchase and I couldn't be happier, especially since I now use cell phones exclusively for my business/employees. My advice is to call them up, describe your situation, and let them help size the system for you. It was not a cheap system that I bought (> $1K) but there is no subscription so it was a one-time cost and it works awesome. For me, it was worth every penny.
