I know this is an old service. But I am sure many of the users still dont know this free service offered by BSNL. While other operators are charging for this service, BSNL is giving it absolutely free. This service helps you to find out who called you while you were unreachable.
You can activate the service in two ways.
Using Phone Menu
Just divert your calls to +9117010. Most probably divert option will be the call settings menu. Select Divert when unreachable or a similar menu.
Using USSD call
This method is more simple. Actually this USSD code also execute the same thing that we did in the first method.
Dial **62*+9117010# from your BSNL mobile.