It might be worth considering AT&T’s 3G Microcell:
AT&T 3G MicroCell acts like a mini cellular tower in your home or small business environment. It connects to AT&T’s network via your existing broadband Internet service (such as U-verse, DSL or cable) and is designed to support up to four simultaneous users in a home or small business setting.
We live squarely in the Twin Cities metro area. Nonetheless, I get only 2-3 bars of coverage on the main floor of my house, and only 1 bar in the basement. Just about every call that I take in my basement is bound to be dropped if it lasts more than 5 minutes, which is a problem because that’s where my home office is. So I’m eager to see how this works.