@Filip Havlicek Tnaks for you suggestion. It worked. It blocked all the SMS that had "hidden numbers" and "unknown numbers". However it also blocked couple of genuine SMS. Example: The ISP's monthly bill SMS, BANK alert SMS. I have couple of Bank SMS in inbox, using those I stored their numbers in contacts so that they will not be treated under "unknown numbers". However now, how do I unblock ISP's SMS? In the log I see his SMS but don't know how to move it to Inbox? so that I can put his details in contacts.