Here is how it works: you choose which operator you want to check. For now, only Tesco Mobile is supported. A window opens where you log in to Samoobsluha.TescoMobile.cz (which opens for you automatically), click through to the call statement, and press a single button with a “pin” (well known from my programs).
The program will then load all pages of the statement and parse them. In my case, with 14 pages, it took about 10 seconds before the result appeared: 
My mom calls even fewer numbers:
The charts are in HTML (more precisely, HTML is the wrapper, the charts are in JS, which generates SVG – free Google charts) and they are automatically saved to disk in the program’s folder, so you can archive them or send them to anyone. As the web browser I use Awesomium.NET, which is a .NET clone of Google Chrome/Chromium.
Here you can see that calls to my mom account for 86.5% of all seconds (4h 37m 53s over the last 90 days), and in the number of calls it is even 87.5%; SMS messages sent to my mom made up 38.9%. The program also calculates how much it cost me, but it does not show that in the chart yet.