How to build Callback service with VoIP

International and Long Distance call rates vary from country to country and from network to network. It is very usual case when calling from Country A to Country B may be much more expensive than calling from Country B to Country A. These differences are typically due to many factors, such as: local regulation, competitive status in the market, and interconnection agreements.

Callback is an additional telephony service which makes use the difference between international calling rates in different countries. It finds its applications in the countries where international calling rates are especially high. In the classical callback case there would be involved another country (Country C), which has lowest international calling rates to both Country A and Country B. The call flow in classical callback would be following:

1. Caller A dials the callback number in Country C;
2. Callback service in Country C would take note of Callers A caller ID, and drop the call without answering;
3. Callback service in Country C would call caller A;
4. Caller A picks up the phone, and enters destination number of called party in Country B;
5. Callback service would then dial called party to Country B from country C;
6. When destination picks up, both parties are joined in conference and call is established.

So in the above setup the combined call rates from country C to A and B are lower than the direct call rate from country A to B. This is the only possibility for callback to be working properly.

Now, in the era of Internet, the VoIP calls are no more originated from specific country. Instead they can originate elsewhere on the internet and enter PSTN at the most convenient point, having the lowest call fees. In this scenario the callback services become even more attractive because the chances of finding lower call rates to country A and country B are much higher than before, i.e. call back service is not tied to any specific country C. Instead, the callback service is located in the "cloud".

Internet and mobile apps allow to simplify the callback initiation process. Apps exists which replace standard phone dialer application on mobile phones, or allow intercepting the dialing by redirecting call to callback application. There are several ways to trigger callback:

1. By data connection. The application sends both caller ID and called party ID to the callback server. The callback server can immediately dial both parties, therefore reducing the connection times.
2. By using CallerID - Called ID mapping. The predefined called party IDs from callers phone book are synchronized with callback service. The application just dials specific number in the callback service number pool, and server maps that number to the called party ID.
3. By sending SMS to the callback service

As one can see, there are now many more options to build callback service with help of VoIP service. Some solutions may require custom build applications to handle different callback scenarios. Check out our Javascript based telehony scription language on how to do it.