This document shows you how to use asterisk to make international calls via the command line. A graphical client like Zoiper can be used additionally to verify that the endpoint number can be reached.
You can download it from the following link: https://packetstormsecurity.com/files/download/127297/asterisk-phreaking.txt
Source: https://packetstormsecurity.com/files/127297/Asterisk-Phreaking-How-To.html