Your pre-paid account would get debited based on your usage.
The talk value of your card is net of Service Tax (12.24%).
The Billing for the calls will be done as per the destination country called and the duration of the call. The Billing would be done in Pulses, where in each pulse is 1 minute, and any call duration will get rounded off to next highest minute.

Now, with the Sify Talk pre-paid service, You can Call your friends, relatives and others abroad for a change and talk on, without having to worry about running huge telephone bills and all this and more from the comfort of your Home