China Mobile continues to be at the top spot with 683.08 million connections, followed by Vodafone Group (386.88 million) and America Movil Group (251.83 million). 

Bharti Airtel (250.04) and Telefonica Group (243.51) are at fourth and fifth position, respectively, Wireless Intelligence said in its 'Mobile operator worldwide group global ranking by connections (Q2, 2012)'. 

Besides China Unicom (which is at the sixth position), the report said Bharti Airtel is the only other member of the top ten to move up the ranking, recording a 13 per cent year-on-year rise in connections to overtake Telefonica. 

Bharti Airtel had become the fifth largest mobile operator in the world following its acquisition of Zain Group's mobile operations across 15 African nations in June 2010, the operator said in a statement. 

It, however, added that Bharti's mobile revenue at $ 3.04 billion in the second quarter of FY12 is significantly lower than the other operators in the top five, "reflecting Bharti's presence in the ultra low-cost, low-margin Indian and African markets." 

The other Indian telecom operators in the report are Reliance Communications, Idea Cellular and BSNL at eighth, fourteenth and twentieth position, respectively. 

While Reliance Communications has maintained its global ranking, Idea Cellular has moved up three places. State-run BSNL's ranking dropped by two places. 

Telenor and Sistema - foreign firms with a subsidiary in India - were at the ninth and fifteenth position, respectively. 

Russia's Sistema Group lost four positions in the ranking, the report said.