Falko Timme writes “In this howto I will guide you step-by-step on how to successfully set up long distance calls service in your Cybercafé, using open source software. The main element is *starShop-OSS, an open source application designed to monitor and bill, in real time, calls made via Asterisk PBX. This service is commonly called callshop or taxiphone.”
Link: howtoforge.com