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Problems with voicemail have forced Telecom to delay the introduction of a single number for mobile customers using their phones overseas.
Telecom customers wanting to roam globally need to take a WorldMode phone, which work on Telecom's CDMA network as well as the more common GSM networks of its roaming partners.
Currently this means having two mobile numbers and voicemail boxes - a Telecom 027 number and a SIM card and mobile number provided by United Kingdom mobile company O2, Telecom's former roaming partner.
Telecom spokesperson Katherine Murphy said Telecom had hoped to introduce its own SIM cards - meaning customers only needed the one phone number - at the same time as it launched new global roaming price plans.
However, live testing of the service revealed "an inconsistency" with the voicemail service.
"We won't be activating Telecom SIM cards until we're completely happy with the voicemail system," Murphy said.
Telecom signed a three-year global roaming deal with Hong Kong mobile operator CSL in April.
The zone-based roaming prices came into effect on Thursday.
