The company, which holds the second mobile phone licence in Iran, had 11.6 million customers at the end of June, almost twice the 6 million customers it had at the end of December 2007 when it had 22.1 per cent of the market.
MTN Irancell's estimation of its own market share provides one of the few insights available into the performance of the Iranian mobile sector.
Telecommunications Company of Iran (TCI), its state-owned rival, only provides updates on its performance sporadically.
If MTN Irancell's estimates of its market share are correct then TCI's share of 68 per cent would mean it had some 24.7 million mobile phone customers at the end of June.
MTN has a number of other subsidiaries in the region. MTN Syria increased its customers by 9 per cent to 3.4 million. The company's Sudanese and Yemeni operations had 2.1 million and 1.7 million customers respectively.