ISD tariff war intensifies; telcos slash call rates Hindu Business Line After slashing 3G tariffs, telecom operators are competing to give the lowest ISD rates. Bharti Airtel is the latest entrant to this price war with a special offer for high-end subscribers. "The major cost for ISD is the carrier cost that has come down consistently over the last one year. The surge in the ISD traffic is directly proportional to the fall in the costs. All operators are likely to bring down rates," said an industry expert.