All the three telecom companies have been booked on charges of criminal conspiracy and cheating under the Indian Penal Code and also under the Indian Telegraph Act for violating the Department of Telecommunications' licencing norms.
The FIR has been filed in a local court on a complaint of Ministry of Communications and IT.
When contacted, Bharti Airtel had no comments to offer while Tata Communications said it would not comment on speculation.
It said the Singaporean company had offered and provided unauthorised ILD services to the Indian customers without obtaining the requisite ILD licence from DoT.
Sources said the actual loss can be calculated after getting the amount collected by illegal ILD Services provided from various Indian customers.
The CBI has said in the FIR that "facts in the complaint disclose commission of offences under Section 120-B read with 420 IPC and section 20 of the Indian Telegraph Act against M/s Singapore Telecommunications, M/s Bharti Airtel Ltd and M/s Tata Communication Ltd. A regular case has been registered for investigation.
