How to know how may calls we used in running month

Is there any facility or method to view the number of calls we made in the current month, as some BSNL BB Combo plans are giving free calls.

1.
Sometime earlier, a number was given to
check the present meter reading. Usually auto response.
Check with your Exchange CC..

2.
You may have to use a call meter as used in PCO's.
3.
or "DIY" (Do it yourself ) Electronic system with calculator.
( Basically counts number of pulses based on time duration set and stores in calculator memory)