Bharti Airtel Ltd, India’s leading mobile carrier by subscribers, posted a 10% rise in quarterly net profit that beat estimates, helped by a surge in data usage by customers.The company, headed by Sunil Mittal, said net profit for the quarter ended 30 September, 2015 rose to Rs 1,523 crore ($234.4 million), up from Rs 1,383 crore in the corresponding period last year. A rapid proliferation of smartphones, led by Chinese brands, has prompted Indian users to use their handsets to access the Internet and demand faster downloads, which are typical of 4G services.India is also seeing an unprecedented demand for fast data as its booming startup industry leans heavily on stable internet connections to get customers.”With the commercial launch of high speed 4G services across 334 towns and roll-out of 3G services … we are now best positioned in the industry to leverage the fast growing data market,” Gopal Vittal, chief executive of Airtel’s India & South Asia unit, said in a statement.Bharti Airtel has been in the lead in bringing fourth generation data services to customers in India, ramping up coverage ahead of rival Reliance Jio’s 4G services launch. Reliance Jio is the telecommunications unit of cash-rich conglomerate Reliance Industries led by Mukesh Ambani. In August, Airtel said it would price its 4G services at existing 3G costs, and the carrier is allowing some users to migrate to 4G for free.These efforts helped Airtel add more subscribers than rivals. Airtel, however, saw a drag from falling voice call charges, same as rival Idea Cellular did last week.As voice calls get cheaper, telecommunications carriers in India are focusing on building their data service networks to cater to an increasing number of customers who prefer using apps to calling.Average revenue per user for voice calls, a key measure of telecom health, dropped to Rs 140 from Rs 158 in the corresponding quarter last year. Average revenue per user from data rose to Rs 193 in the quarter, up from Rs 150 during the July-September quarter in 2014. Analysts on average expected the company to post a net profit of Rs 1,150 crore, according to Thomson Reuters data.Total revenue rose 4% to Rs 23,836 crore for the second quarter from a year earlier. Mobile data revenue grew 60% during the quarter.