CORRECTED - India Tata Tele to bill roaming calls per second

(Corrects headline to 'calls per second' from 'calls per minute', corrects currency conversion in paragraph 3)

MUMBAI, Nov 22 (Reuters) - India's No. 6 mobile services provider Tata Teleservices [TATASL.UL] on Sunday extended its per-second billing scheme to roaming calls as well, as the tariff war in the world's fastest-growing wireless market heats up.

On Friday, industry leader Bharti Airtel (BRTI.BO: Quote, Profile, Research) introduced a new billing plan that cut mobile roaming rates by nearly 60 percent, depressing the company's shares.

From Monday, Tata Teleservices, 26 percent owned by Japan's NTT DoCoMo (9437.T: Quote, Profile, Research), will charge 1 paisa per second for both incoming and outgoing calls made while roaming across India, irrespective of the network used, it said in a statement. There are 100 paisas in 1 rupee ($0.022).

Tata Teleservices was the first to launch per-second billing, deviating from the industry norm of per-minute billing. The offer was a roaring success as the firm topped the new signings for three months in a row.

However, the price war, aimed at grabbing new users ahead of fresh entrants waiting in the wings, has raised concerns about telecom firms' profitability. Four new firms, including ventures funded by Telenor (TEL.OL: Quote, Profile, Research) and Etisalat ETEL.AD, are set to start services this year adding to the existing 11 operators. (Reporting by Bharghavi Nagaraju; Editing by Jon Loades-Carter) ((bharghavi.nagaraju@thomsonreuters.com; +91 22 6636 9059; Reuters Messaging: bharghavi.nagaraju.reuters.com@reuters.net)) (If you have a query or comment on this story, send an email to news.feedback.asia@thomsonreuters.com)