Incoming international voice calls dropped 50 percent to 3.5 crore minutes a day in two years thanks to illegal call routing channels, depriving the government of thousands of crores of taka every year.

For every minute of incoming international voice call $0.0175 cents (about Tk 1.5) come to the country, and mobile phones are the main channel for routing calls.

"Mobile operators will have to shoulder responsibility," said Md Mustafa Kamal, director general of engineering and operation division at the Bangladesh Telecommunication Regulatory Commission.

In 2016, all mobile connections were biometrically verified, and yet illegal call routing increased.

Between October 14 and November 1, a total of 42,150 SIM cards were seized in raids by the BTRC in association with law enforcement agencies in the capital and the port city and 24 people were arrested on charges of running illegal voice over internet protocol (VoIP) operations.

Equipment worth Tk 1.23 crore was seized in the 23 drives in Dhaka and Chattogram, and the authorities also have filed 28 cases in this connection.

"The mobile operators never ran any investigation against their retailers and distributers," Kamal said at a press conference yesterday to brief on the outcomes of the raids.

Of the SIMs confiscated, 16,812 were of Robi and Airtel, 15,939 Teletalk, 6,176 Banglalink and 3,233 Grameenphone.

If one lakh SIM cards are used every day for 16 hours for illegal call termination, they can appropriate Tk 6-7,000 crore for themselves and the government is directly deprived of more than Tk 2,500 crore a year.

The mobile operators may face legal action under the telecom act along with charges of money laundering, Kamal said. BTRC is now using the latest technology to sniff out illegal transmission of international calls, said Md Jahurul Haque, its acting chairman.

Representatives of all four mobile operators tried to clear their position but the regulator did not accept their explanation.

Earlier in September, BTRC seized 10,947 SIM cards from Dhaka, of which 5,075 SIMs were of Teletalk, 3,897 of Robi, 1,414 of Grameenphone, 426 of Banglalink and 120 of private land line operator Rankstel.

BTRC said their drives have saved the country Tk 867 crore.