Call Back System
The Call Back system is a simplified "Calling Card" like system. But works on a different principle. Some countries, it is impossible to call certain numbers, and/or might be far cheaper for inbound calls than outbound calls. In this situation, an inbound call can be triggered by calling a certain number (which goes to the IVR). This system will recognize the incoming CLI number to a user account, and call back the number previously configured in system (could call back the same number of different number).
Then, the user can enter destinations to call via the IVR system.