Chairman of Reliance Industries, told shareholders that what he called a "welcome offer" would last until the end of the year. The company has announced a range of tariff plans that will apply from January 2017.
Reliance Industries – which is not related to rival operator Reliance Communications (RCom), run by Ambani's brother Anil – has invested around $20 billion in its new nationwide 4G network.
Reliance Jio is setting data prices at 50 rupees ($0.75) per gigabyte. Services are officially launched on Monday 5 September.
Stocks of rival operators, including Bharti Airtel, Idea Cellular and RCom, were affected on India’s National Stock Exchange after Ambani’s announcement. Bharti Airtel was up slightly, but Idea and RCom were down 2.1% and 1.5% respectively.
Jio is offering free SIM cards for the new service from its stores and other outlets across India, and is promising "unlimited HD voice, video calls, SMS, high-speed data and access to Jio Apps".
Ambani told shareholders he would "transform India from a high-priced data market to one with the lowest data rates anywhere in the world". He said he hopes for 100 million customers "in the shortest possible time".