The Telecom carrier company has direct access to the Line Information database (CNAM database). This database holds the details about a phone number and related information. Direct access rights are given to Telecomm carriers only. Thus it is easy for them to detect the source or the person from where the unknown call is generated. They can even find out the anonymous calls labeled as 'Private'. If the carrier company is subscribing to the access to the CNAM database, then the carrier level blocking is more efficient and reliable. The third-party apps are to be used only after understanding the complete details and going through the reviews added by the users.