The racket, which used the internet-based Voice Over Internet Protocol, bypassing the mobile phone/landline phone networks, was active for the last four months, and caused a loss of at least Rs 49.14 crore in revenue to the Department of Telecom, police said.
The raids were carried out at Shivaji Nagar, Mankhurd, Govandi and Trombay here.
Indian nationals living in Saudi Arabia used these illegal telephone exchanges to speak to their relatives here, police said.
"As per the DOT officials, the loss of revenue from calls received from foreign countries through three SIMBOXes during the last four months was Rs 49.14 crore. Calculation of calls received through remaining 44 SIMBOXes is going on," said Deputy Commissioner of Police Dilip Sawant.
The accused used Chinese equipment and technology to set up the exchanges. The mastermind of the racket had visited China for 'training', he said, adding that further probe was on.