MTN's home market now only accounts for 26percent of its customer base, September subscriber figures for the cellphone network released yesterday showed.
Total subscribers in all 21 countries MTN now operates in grew 12percent to 54million.
MTN said it only counted subscribers who had made at least one call on its network within the last 90 days.
In South Africa, MTN is still some way behind Vodacom's subscriber numbers dating back to June. MTN had 11,5million prepaid subscribers in September versus Vodacom's 21million in June.
MTN's prepaid numbers have been inflated slightly because it now counts community phones as prepaid customers.
This change in accounting helped its prepaid subscriber numbers grow 4percent.
Vodacom reported its community phones at 96000 in June.
Though MTN has less prepaid customers, it averages more money per customer than Vodacom. MTN's average revenue per user for prepaid is R89 against Vodacom's R58.
MTN's domestic contract customer numbers remained flat at 2,5million from the previous quarter, lagging Vodacom's 3,2million in June.
Vodacom's more aggressive entry into the wireless broadband market helped it average R488 per prepaid subscriber against MTN's prepaid revenue of R393.
Yesterday's release by MTN showed its fastest growing market was Iran where its subscriber base nearly doubled to 3,7million, followed by Afghanistan.
Subscribers in Uganda increased 12percent to 2million through more competitive pricing. Cameroon increased subscribers by 15percent to 2,2million through increased marketing.