Requirements:

Server
Access Numbers
Termination

Servers:

First of all you need a Server for Calling Card on which you can configure your calling. There are different soft wares that provide calling card. Some of the most used soft wares are listed below:

  • VoIP Switch (They are basically server providers that provide different servers for calling card purposes with GUI Interface).
  • A2Billing (One of the leading Calling card software with GUI Interface).
  • Freepbx (This software is also have GUI Interface).

All the above mentioned products have GUI Interfaces. The simpler and cheapest solution of Calling Card is to install any linux OS (CentOS, Ubuntu, Redhat) and install Asterisk on it. After Installation of asterisk configure calling card on it and you are good to go. There are different versions of Asterisk which you can install on your Server. The most recent stable version is Asterisk 11.

Access Numbers:

An Access Number is a regular number in your area that you can use to access our system and make international calls.
For example if you are looking to setup Calling Card for UK Numbers then you need to buy UK access numbers that you can setup with your server and use them for Calling Cards.

Termination:

Call termination, also known as voice termination, refers to the routing of telephone calls from one Telephone Company, also known as a carrier or provider, to another.
The terminating point is the called party or end point. The originating point is the calling party who initiates the call.
This term often applies to calls while using voice over Internet protocol (VoIP): a call initiated as a VoIP call is terminated using the public switched telephone network (PSTN).
In such cases, termination services may be sold as a separate commodity. VoIP call termination is a word that is fast spreading across the globe among all age groups—from individuals to small businesses to corporations and enterprises.
It simply means providing a path or route through which voice can be transmitted or sent over Internet.

Installation and Configuration: (Asterisk & Calling Card)

After installing OS on your server you have to install Asterisk on your server. You can install asterisk by following the commands mentioned in the link below:
http://blogs.digium.com/2012/11/05/how-to-install-asterisk-11-on-centos-6/
After installing Asterisk you have to configure the Calling Card by the following commands: First download the Asterisk Billing Package
http://sourceforge.net/projects/asteriskbilling/
After downloading the package perform the following commands, make install, Copy prepaid.conf to your /etc/asterisk dir and modify to suit your needs Populate the database with cards, providers, tariffs, tariff rates etc.. To make it work.
Record your own sound files (prepaid-card-expired, prepaid-zero-balance, prepaid-you-have, prepaid-and, prepaid-cents, prepaid-dollar, prepaid-dollars, prepaid-card-in-use, prepaid-no-aaa, prepaid-final)Configure an extension with the Calling Card app and you’re in business!

Example:

exten => s,1,CallingCard