MM02 attracted half a million new punters during the last quarter, bringing its total customer base to just under 19 million.
In Germany and the UK the mobile phone company also reported that punters were spending more, although average revenue per user (ARPU) remained flat in Ireland.
In the UK, the number of 02 punters increased ten per cent (258,000) on the previous quarter to 12.3 million with each of them spending, on average, around £254 on mobile stuff.
Specifically, O2's contract punters spent around £504 - essentially flat compared to the previous four quarters - while its pre-pay punters increased their spending by 17 per cent to £128.
In Germany, O2 added 225,000 new customers in the three months to the end of June taking its total base to a smidgen over 5 million. ARPU was also up a tad too.
In a statement mm02 chief exec Peter Erskine said the company has "maintained our momentum in both the UK and German markets, in the face of increased competition".
However, he accepted that there were still "challenges ahead" referring in part to increased price competition from the likes of 3 in the UK and the recent regulatory ruling from Oftel that should see the cost of mobile phone calls fall for consumers.
Shares in MMO2 were down 1.25p (2.31 per cent) at 52.75p by mid morning. ®