What is the Call Barring service?

This service lets customers bar calls from specific numbers and also from specific countries.

Call Barring Service
How can I subscribe the Call barring service?
What features are included with the chargeable barring service?
What features are included with the free barring service?
Is the Call Barring service free?
How is the Calls Barring Service different from what I already have on my device?
How can I manage the Call Barring service (add and remove countries and numbers)?