Were you using ISD in BSNL prepaid mobile services? And now surprised that ISD is not working.
BSNL deactivated the ISD services in prepaid mobile services from Dec 1, 2012.
It is very easy to activate the ISD Bsnl prepaid services.
Just send an SMS ISD Y to 52271.
It will be activated in 24hrs time. If not, contact the BSNL customer service.