There will also be a sharp spike in the number of 4G subscribers in the country, the industry body said.
India is expected to have nearly one billion unique mobile subscribers by 2020 up from 616 million such users in June 2016, according to a latest report by global industry body GSMA.
The report also projected a spike in adoption of 4G services in the country, saying the number of 4G connections would grow to 280 million by 2020 from just three million at the end of 2015.
"...at the end of June 2016, 616 million unique users had subscribed to mobile services in India, making it the second-largest mobile market globally, with almost 1 billion unique mobile subscribers expected by 2020," the report 'The Mobile Economy: India 2016' said.
Unique subscriber refers to one individual who has subscribed to mobile service and that person may have multiple mobile connections.
The GSMA report forecasts improving affordability, falling device prices, operator investments in network coverage and quality will help deliver an additional 330 million unique subscribers in India by 2020.
This will lift the country's penetration rate to 68% of the population by 2020, up from 47% in 2015.
Notably, during the year, India overtook the United States to become the world's second-largest smartphone market with an installed base of 275 million devices, the report added.
"India is expected to see a significant uptake in mobile subscriptions, broadband and connectivity by 2020, marking a period of rapid development of the country's mobile economy," it said.
India is also seeing an ongoing technology shift to mobile broadband services, it said adding that the number of 3G and 4G mobile broadband connections is projected to cross 670 million by 2020, or 48% of the total connection base.
"In addition, the industry is set to invest heavily, with operator capex growing to $34 billion (Rs 2.3 lakh crore) for the period 2016 to 2020.
The Indian mobile industry's contribution to GDP is expected to grow to Rs 14 lakh crore ($210 billion) by 2020, from Rs 9 lakh crore ($140 billion) in 2015.
The figure accounts for both the direct economic activity generated by mobile operators and the ecosystem of mobile industries in India.
"To fully realise India's tremendous market potential, review and reform in key areas, including modernising regulation and long-term planning for spectrum allocation, would accelerate mobile broadband access and adoption across the country," Mats Granryd, Director General of GSMA said.
About 430 million people had access to mobile internet services as on mid-2016, and this is set to touch almost 670 million by 2020.
This still lags the regional average of 63% penetration, and the survey found lack of awareness and locally relevant content to be the biggest barriers to internet usage.
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