This leaves four relatively smaller players - Halotel, Zantel, TTCL and Smart - fighting amongst each other for the remaining 14 per cent of the market share.
According to the Tanzania Communications Regulatory Authority (TCRA), Vodacom Tanzania ended 2018 with a market share of 32 per cent of total voice telecom subscriptions, unchanged from a year ago.
Vodacom was followed closely by Tigo Tanzania, which increased its market share to 29 per cent from 28 per cent previously.
But among the 'big three,' Airtel Tanzania was only top mobile operator to shed its market share, which shrunk from 27 per cent in 2017 to 25 per cent in 2018.
The government announced this month that India's Bharti Airtel has agreed to give part of its stake in Airtel Tanzania to the state, raising the nation's holding in the mobile phone operator to 49 per cent from 40 per cent.
The announcement followed talks at State House in Dar es Salaam between President John Magufuli and Bharti Airtel Chairman Sunil Mittal to resolve a longstanding dispute over ownership of the Tanzanian mobile operator.
"We have in principle agreed to move forward with a new arrangement of shareholding of 51:49 -- where Airtel will now drop from 60 per cent to 51 per cent and the people of Tanzania through the ownership of the government of Tanzania will own 49 per cent," Mittal said after talks with Magufuli.
State House said the government will not make any payment to Bharti Airtel for acquiring the additional shares.
The government, which initially demanded 100 per cent ownership of Airtel Tanzania, is also claiming dividends from the telecoms firm.
As part of a new deal, Airtel will pay the government a total of 60 billion shillings over a five-year period.
Magufuli had said in 2017 that TTCL owned the local subsidiary of Bharti Airtel outright but had been cheated out of shares.
Bharti Airtel had disputed this, saying it received all the required approvals from the state when it bought a 60 per cent stake and had complied with all government rules.
The growth of Halotel
TCRA's statistics show that the total number of mobile phone subscribers grew to 43.62 million by the end of last year, up from 40.08 million by the end of December 2017.
Mobile phone penetration in Tanzania now stands at 81 per cent, up from 78 per cent a year ago.
This means that mobile network operators added over 3 million new subscribers in just one year, with most of these snapped up by Tigo and Vodacom.
Vodacom saw the number of its subscribers climbing to 14.14 million in 2018 from 12.86 million a year ago.
Tigo posted 12.58 million customers last year, up from 11.06 million in 2017.
This translates into Vodacom adding 1.3 million new subscribers in one year, while Tigo added 1.5m customers.
On the other hand, Airtel added less than 100,000 new subscribers in a whole year while its rivals made big gains, thus causing its market share to decline.
Halotel saw its market share in 2018 declining slightly to 9 per cent from 10 per cent previously, but increased its subscriber base to 3.94 million from 3.79 million in 2017.
TTCL, which had 0.711 million customers last year from 0.429 million in 2017, saw its market share increase from 1 per cent to 2 per cent.
Zantel has a 3 per cent market share, while Smart has a market share of just 0.3 per cent, according to latest TCRA statistics.
Vodacom, Tigo and Airtel also dominate the mobile money business, which has become an important revenue stream for telcos.
The number of internet users grew to 23.14 million last year from 22.99 million in 2017, representing a penetration of 43 per cent.
The TCRA data shows that over 96 per cent of Tanzanians access the World Wide Web using mobile phones and other wireless devices.