New Delhi, July 19 -- Mukesh Ambani-controlled Reliance Jio has vaulted past Bharti Airtel to become the country's second-largest mobile telephone company by user base. Considering Jio's growth strategy, this was inevitable. Jio launched its commercial services-entirely on 4G technology-in September 2016, signing up millions of subscribers in a matter of moths with its initially-free data and voice service. The latest data put out by the Telecom Regulatory Authority of India shows Jio has about 323 million subscribers, as of 31 May, ahead of Airtel's 320.4 million and behind Vodafone Idea's 387.6 million users....