Using a Cellphone in a Basement?

Nimsoft asks: "I recently moved into a basement flat and as a result I get no cellphone coverage in there. This is incredibly frustrating as my cell provider is so much cheaper than landline offerings I rely on my cell as my primary means of telecommunications. I can pick up a signal the second I step out of my front door and friends on other networks can sometimes pick up a weak signal within my flat. What would the geek solution (must be cheap!) to this issue be? Would attaching a larger antenna to my phone work, or can I hack together some sort of repeater and put an antenna outside somewhere?" While thousands of offers of repeaters and signal boosters are only as far away as the nearest Google search, what recommendations or experiences would you care to share on the subject?