Officials say using an Indian SIM card is costly as BSNL treat calls to Bangladesh as international calls.
BSNL's General Manager (Tripura) Deb Kumar Chakraborty said, "We block such calls using Time Advancement System because it is illegal to talk to anyone in a foreign country without the facility of international call in his or her phone".
An exporter from India here said on condition of anonymity that traders often use Bangladeshi SIM cards sitting in the heart of Agartala though it is illegal.
"Sit on the roof top of any tall building and speak to your business partner or friends and relatives. No problem, because the sound is clear. It is risky but it is difficult to identify," he said.
The BSNL's official said the matter is under examination by security agencies of the central government.
"If Bangladesh want they can stop it by using the same Time Advancement System like India," Chakraborty said.
