"We have acquired 5-6 lakh 3G subscribers. We are witnessing a good data usage of over 1 terabyte per day from a single city," the company's President for Mobile Services, Atul Bindal, said after launching its 3G service in Mumbai.

Mumbai is the 11th city where Airtel has launched its services and the company is targeting a rollout in 40 cities across 13 telecom circles where it has secured a 3G licence by March-end. The company is targeting a 3G presence in 1,000 towns and cities by FY12-end, he said.

3G offers better bandwidth which enables heavy data transfer. Mobile firms have paid heavy fees in an auction to secure the spectrum for roll-out of the services.

Bindal said the average revenue per user (ARPU) numbers will definitely "firm up" under 3G as the conventional voice service rates have plummeted due to competition.

Bharti, India's largest GSM company by subscribers, currently gets 9 per cent revenues from data services, which will "significantly" rise as 3G becomes operational.

For the Mumbai circle, Bharti has invested in erecting 1,300 3G sites or towers which are over and above 3,100 2G sites it has, the company's Executive Director, Deepak Mehrotra, said, adding the 1,300 sites are enough to suffice the requirements of 80 per cent of users.