Boost Signals of mobile network
What phone do you have? 

If it's a smart phone, chances are there is a free app that can display RSSI (signal strength). You can use this number to make a map. You'll find that buildings and trees pose the most interference, and the higher you are the better the signal. You can even come up with a 3d map if you are ambitious :) Just use a smartphone to map the RSSI or SNR.

To boost the signal, the easiest approach is to attach a high gain antenna. A Yagi or even a parabolic dish antenna if you want to get the ladies' attention. :)