Paul Reynolds said its XT mobile network was still growing "pretty healthily" in spite of a series of network outages since late last year.
Reynolds said connections at March 31 are at 585,000 - up 128,000 from the end of December.
Just over half of those connections are contract customers.
Telecom had previously indicated it aimed to migrate a third of its 2.25 million mobile customers by the end of the current financial year - roughly 750,000 customers by June.
"We're seeing reasonable growth despite recent issues," Reynolds said.
Total connections across both its XT and old CDMA network were down 19,000 for the March quarter.
Reynolds said these were primarily low-value, CDMA pre-pay customers.
He said corporate connections managed by its Gen-i business were "stable with a pipeline that we can see to come with further growth on XT".
Several key business signings from rival Vodafone, including 1500 Fonterra staff, are on hold until the network issues have been resolved.
Telecom said the outages would only have a short-term effect on revenue.
Chief financial officer Russ Houlden described the XT outages as a "road bump" and reiterated the company's long-term goal of becoming number one in mobile.
XT network showing reasonable growth despite outages, says Reynolds
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