When I bought my new house in April, one of the most annoying things I discovered was that I got virtually zero cell service inside the house. The house is down in a valley and thus has no good line-of-sight to any cell towers. Inside the house I'd get 0-1 bar, and outside on the front lawn I'd occasionally get 2.
To try and remedy this situation, I had two choices: get a landline (with yet another phone number and at least $20/mo) or I could go with a "smarter" solution and get a cell repeater/booster. I found this gem after doing some research online: the YX510 dual-band cell repeater.
So for just over $300 I got this fairly large box containing an 18" external antenna, 35' of high-grade coax cable, and a chunky little box for inside with a little 6" antenna.
I went up on the roof of the house and found that I got 4 bars near the back of the house. So I mounted the external antenna at the top of an 8' 2x4 that I strapped to the side of the house. Then I ran the provided coax around the house into the attic, where I mounted the interior box.
I should note that I took care to put as many physical barriers as possible between the interior and exterior antennas, to prevent feedback loops. In my case, I was able to get 2 sets of shingles and 3 walls in between the antennas.
Finally, I found a good place to plug in the provided wall-wart, then spliced in an extension into the power cable (the provided one was only 4' long). Then I plugged the base unit in, and voila! I now get 4-5 bars all over the house. No more dropped calls, no more "are you there?" when talking to somebody. And I don't need to get a landline.
Highly recommended to anybody that is in a similar situation (bad cell service somewhere but with an easily accessible location nearby with good cell service).
edit: Here are pics of the setup.