With populations in Asia, and notably India, on the rise, the number, which stood at 4.8 billion a year ago, should mushroom to 5.7 billion, or three quarters of the world's population, by 2020.
Asia will account for around half total growth, according to GSMA's 'Mobile Economy' report with India alone adding some 310 million new subscribers in the coming three years.
The study also showed a trend towards mobile broadband networks and smartphones, said the study, which highlighted the mobile industry's growing contribution to economic activity and social development.
"Mobile is a global platform that today supports two-thirds of the world's population, delivering the connectivity and infrastructure that is powering new digital economies and addressing socio-economic challenges," said Mats Granryd, GSMA director general.
"Our latest Mobile Economy report reveals how the near ubiquity of smartphones and high-speed connectivity is enabling innovation in areas such as artificial intelligence and driving the digital transformation," added Granryd, citing trillion-dollar investment in global networks since 2010.
That investment had seen the telecoms sector account for a 4.4% share of world GDP worth $3.3trn dollars last year, rising to a 4.9% share by 2020, for economic value equivalent to $4.2trn.
The report said the mobile ecosystem last year employed 28.5 million people directly or indirectly, a figure it said would rise to 30.9 million by 2020.
It added the sector would contribute $500bn in tax receipts by 2020, up from $450bn last year, not including revenue from spectrum auctions, worth almost $19bn in 2016.
Operators are forecast to invest a further $700bn by 2020 when 5G connectivity is set to bring ever faster data connection.
Ahead of 5G - forecast to enable subscribers to download a full HD film in less than one second - 4G has been steadily becoming the norm, rising from current market penetration of 21% to 41% by 2020.
GSMA said 2016 saw 580 4G networks launched in 188 countries covering 60% of the world population.
The organisation added 55% of overall connections were now running on mobile broadband (3G/4G) networks, which are forecast to account for almost three-quarters of connections by 2020.