I am looking for a way to boost the cell phone service at my office. We are in the basement level (concrete walls and ceiling, half windows on one side). Just outside the office (near downtown minneapolis), I get full service. In the basement, I either have one bar or no signal. Is a cell phone repeater the best way to go to boost the reception? If so, what kind? What about those 6" external antennas that plug directly into your cell phone? Do those work at all?

I have T-Mobile service ( i believe the frequency is 1900mhz), and use a t-mobile dash. Also another guy in the office has T-Mobile and uses a Samsung Blast, and another has Qwest with a Nokia phone. What frequency does Qwest use? Would we need a dual band cell phone repeater? What is the difference between gsm and cdma?