A major global roaming network glitch is affecting Telecom and 2degrees mobile customers.
The fault means that affected customers overseas can't use their phones properly. Customers have been sporadically unable to make calls, texts or access data since yesterday morning.
On their website, Telecom posted that they are trying to solve the problem.
"Our apologies, our international roaming service is experiencing difficulties worldwide," the statement said. "Roaming customers may be unable to make or receive calls, send or receive text messages or data."
On their website, Telecom recommended if users need to make urgent calls, texts or access data, they log into Wifi capable services or obtain a local SIM card.
2degrees has also posted similar messages.
Users of the services have taken to Twitter with their concerns.
"My partner is in oz at the moment and his phone has stopped roaming - his workmates too. will this be fixed soon? Pls :-)," wrote Twitter user Anjuli.
An automated message on Telecom's service phone number says they are giving the problem "the highest of priorities."