General Question: FreePBX+Asterisk + X = International calls?

Though I have a knowledge about Voip, but they are as consumer. So as developer I have almost no information about how to build own system… And while searching about it, I come accross to FreePBX and Asterisk, almost in all voip related services. But still couldn’t make sure is it all what neeed to create own voip system and make internationall at no cost?

What and how much investment maybe needed to create own system, for personal use (no calling cards, customers, billing system etc. needed) ?

All answers are appreciated.