Telecom has traced the source of abusive text messages sent to its customers to its own call centre in the Philippines and says the messages are irresponsible.
The messages containing the f-word were sent to five customers in New Zealand.
Four people at the company's outsource partner in Manila have been traced by Telecom's fraud and technical teams and have been suspended.
Some 800 customer service staff work for Telecom in Manila. The individuals who sent the messages worked for Manila Sitel, which claims to be the No 1 global contact centre provider.
Telecom head of external media Mark Watts said on Friday the company has apologised to the customers concerned, but would not say if it had offered monetary compensation.
XT network upgrade on hold
Telecom has put upgrades to its XT network on hold after the work triggered a further network failure.
Upgrades on Thursday morning caused a loss of service in New Plymouth, Upper Hutt and Wairarapa.
Telecom says the fault happened after 20 cell sites were connected to a new part of its infrastructure, designed to increase network capacity.
Service was restored by mid-afternoon, but the upgrade is now on hold until Telecom knows exactly what caused it.
It is the latest in a string of problems for the XT network which began operating in May 2009.
The network had a major failure in mid-December and another in late January in which up to 200,000 customers south of Taupo were cut off for up to three days.