KARACHI, Dec 19: A large number of unlisted telephone numbers are used by officials of various intelligence agencies and law-enforcement bodies, Dawn learnt here on Wednesday.

Well-informed sources in the Pakistan Telecommunication Company told Dawn that only the PTCL director-general was authorized to issue unlisted telephone numbers on request from the intelligence outfits and law-enforcement agencies. They added that the unlisted telephone numbers could also be issued to high-level government officials in “special cases”.

Sources in the four mobile companies operating in the city told Dawn that the mobile companies also issued unlisted numbers. “As a matter of fact, it is easier to obtain an unlisted mobile number than an unlisted land line,” they said.

Senior PTCL officials said no follow-up action was taken once an unlisted telephone number had been allotted to a person on request. “The number of unlisted telephone numbers keeps on increasing. No government, military or otherwise, investigates the fact that the unlisted telephone numbers issued provisionally are never returned by officials,” the sources said.

Other sources in the PTCL also confirmed that they never received a request for stopping an unlisted number.

The sources said the unlisted telephone numbers were used by officials of the Intelligence Bureau, Inter-Services Intelligence, Military Intelligence, Crime Investigation Agency, Special Branch of Police, corps headquarters, etc.

They added that those authorized to use unlisted telephone numbers did not ensure that the telephone sets remained out of bounds for lower-level staff.

“Peons and clerks in the offices of intelligence agencies know which telephone sets are unlisted. They use the sets when their bosses are not around,” they said.

They added that unlisted telephone numbers at the residence of high-level officials were at times used by their family members as well.

PTCL officials said when the caller’s line identification device read “Toll”, it meant that either it was a long-distance call or it was from an electromechanical device (better known as analogue telephone numbers). They added that when the caller’s line identification device read “Private” or “Blocked”, it meant that the call was from an unlisted telephone number.

When asked how a normal telephone number became unreadable for a caller’s line identification device, the PTCL officials said a small command (called CLIR or caller’s line identification restricted) disabled the CLI device from reading the telephone number.

They added that the procedure was not foolproof as even an unlisted telephone number could be found out at the telephone exchange. “In order for a call to be accepted by a telephone exchange, it must reveal its identity. Because of the CLIR command, the caller’s line identification device fails to read the telephone number. But at the exchange, the identity of the call could be found out easily,” they explained.

PTCL sources told Dawn that the users of Integrated Services Digital Network could also employ the facility of calling line identification restriction line identification device, the PTCL officials said a small command (called CLIR or caller’s line identification restricted) disabled the CLI device from reading the telephone number.

They added that the procedure was not foolproof as even an unlisted telephone number could be found out at the telephone exchange.

“In order for a call to be accepted by a telephone exchange, it must reveal its identity.

Because of the CLIR command, the caller’s line identification device fails to read the telephone number. But at the exchange, the identity of the call could be found out easily,” they explained.

PTCL sources told Dawn that the users of Integrated Services Digital Network could also employ the facility of calling line identification restriction.