You obviously haven't seen the commercial with the guy curled up on top of his file cabinet to get the cell phone to work.

There is a device made that might work, but I hesitate to recommend something I haven't played with.  Wilson, and I am sure others, makes a bi-directional cell phone repeater.  You place an antenna inside the building and an antenna outside the building and it makes life wonderful.  www.Wilsonelectronics.com

I like the concept, I just don't know how well it works.  Quoting the Wilson web site All models require at least one outside antenna, one inside antenna and two cables to connect the antennas to the amplifier. The cables must be long enough to separate the two antennas by a minimum of 75 feet