But, mobile number portability (MNP), which was launched in a northern state in late November and nationwide from January 20, was not a "game changer" for the industry, the Cellular Operators Association of India (COAI) said in a statement.
The COAI said less than 5 million subscribers, or less than 1 percent of the country's total customers, had opted to switch carriers.
Idea comes second gainer, Airtel third
Of these, a net 192,761 customers switched to India's third-largest mobile carrier Vodafone Essar, while sixth-ranked Idea Cellular was next, with net gains of 150,789 customers.
RCom lost 306,417 customers
Top mobile operator Bharti Airtel gained a net 148,215 customers in MNP, but No. 2 Reliance Communications was a net loser of 306,417 customers, data showed.
With 771 million mobile subscribers as of January, India is the world's second-biggest market for mobile services and with monthly additions averaging 19 million in the past one year, it is the world's fastest growing market.