Further intensifying the tariff war, Bharti Airtel on Tuesday introduced pay-per-second plan on its virtual calling card service ‘Airtel CallHome’ for its customers in the U.S. The $ 6.99 plan comes with an administration fee of 49 cents, offering customers a tariff of just 0.03 cents per second. The plan has a validity of 30 days. Airtel CallHome has so far been available in the U.K., Canada and Singapore.