How to Lock STD/ISD facility in BSNL Landline Numbers.
For 100% protection against improper use, you can lock your telephone electronically. Here, you only know the secret code. You can lock/allow Local, STD or ISD calls in many way viz. all calls allowed, only local calls allowed, only STD & Local calls allowed, all outgoing calls barred etc.
later on, if anyone forgot the code then visit ur nearest BSNL exchange to get it reset again.