Reliance Communications, second-biggest mobile carrier, signed up 2.5 million cellular users in May. The company had a total of 138.7 million mobile subscribers at end-April.
Vodafone's Indian unit, which is the country's third-biggest mobile carrier, also added 2.45 million subscribers in May to have a total of 139.4 million, the Cellular Operators Association of India said in a statement.
Fifth-ranked Idea Cellular gained 1.8 million mobile users in May to a total of 93.8 million.
Also read: India adds 14.5 million GSM subscribers in March
Telenor's India unit added 1.14 million mobile subscribers to reach a total of 25.4 million.