I had a large church ask Me the same question, I did not have a answer but I sent them this info
http://en.wikipedia.org/wiki/Cellular_repeater I do see things advertized that allegedly will help, I "am sure on this list We will have someone with more knowledge about it Good Luck Don KA9QJG We converted an old Kroger grocery store into a charter school. The building has metal roofing and lots of steel beams, making it very difficult to get a good signal on our Nextel and At&T cell phones. So far we have installed antennas and amplifiers, to no avail. We would like to pay someone to visit the school and make everything work. Any suggestions. R. Dale Dowell, CFO Focus Learning Academy