The IPO is expected to raise between $2 billion–$2.5 billion, Reuters previously reported, which, at the upper end, would make it India's biggest stock market listing since state-owned Coal India Ltd raised $3.5 billion in 2010.

Deutsche Bank, HSBC and ICICI Securities have won joint book-runner roles, the people added, declining to be identified as the information is not public. Vodafone is likely to launch the IPO early next year, they said.

The deal offers a rare opportunity for international banks in a market where equity capital raisings worth more than $1 billion are uncommon and where stock underwriting fees are amongst the lowest in the world.

Vodafone said in November it had started preparations for floating its Indian subsidiary. IFR, a Thomson Reuters publication, said in a report the IPO is expected to raise $2 billion-$3 billion.

The company was not immediately available for comment outside its regular business hours when Reuters attempted to contact it on Saturday.

Vodafone, India's second-largest mobile operator behind Bharti Airtel, had raised the prospect of a listing in India as early as 2011. The company is one of the largest corporate investors in Asia's third-largest economy and is expected to use the proceeds to buy additional radio spectrum and further expand its operations across India's crowded and cut-throat telecoms market.

Indian mobile phone operators have been spending heavily in setting up fourth-generation (4G) mobile broadband data networks to meet expected demand.

Vodafone entered India in 2007, when it acquired a majority stake in Hutchison Essar and since 2014 has wholly owned Vodafone India, which operates in a market that has over a billion mobile subscribers – the second-biggest market in the world behind China.

Reuters reported last week that Vodafone had invited foreign and Indian banks to pitch for the Indian IPO.

Kotak Investment Banking is a unit of Kotak Mahindra Bank. All six banks did not immediately respond to Reuters' requests for comment.

(Reporting by S. Anuradha of IFR and Sumeet Chatterjee; Additional reporting by Elzio Barreto; Writing by Denny Thomas; Editing by Muralikumar Anantharaman)

By S. Anuradha and Sumeet Chatterjee