With most New Zealanders moving to mobile phones, the nation's copper network is slowly being phased out, with one of our biggest telcos planning to pull the plug next year.

"No landline. No landline for ... five years maybe," one woman tells First Up.

"It's fine. Don't miss it. I thought I would but I don't miss it. Even for us old ladies. It's a thing of the past. We all have cellphones."

Another, younger woman interviewed by First Up says her parents still have a landline.

"They answer it, no matter who it is. Which I just never would. I don't answer my cellphone if it's an unknown number."

One NZ (formerly Vodafone) chief technology officer Tony Baird says they are getting set to change.

"The old copper telephone exchanges, the ones in our network, we've got five of them. We deployed them in the '90s and the early 2000s, and we're in the process of decommissioning them."

Baird says that system will be finished some time next year. The decision has been a long time coming, he says.

"The cost of electricity, the efficiency, the floor space they take up, and the number of customers that actually want and use copper landlines is all becoming quite prohibitive."

Baird points to a graph which shows a steady decline in users, with most people moving to mobiles.

"We've got 2.4 million mobile devices out there," he says. "Normally there's more than one mobile per household, everybody has their own mobile, and landlines are really a fixed, static service so people are moving off them."

However, not all phone calls from next year will be from a mobile phone.

According to Commerce Commission figures, there are still around 573,000 landline services in New Zealand.

The majority use the "Voice over Internet Protocol" - known as VOIP, which was first introduced around 20 years ago.

VOIP uses a landline-style phone number on a traditional handset, but runs through fibre internet rather than the copper phone line.

"Voice over internet will remain. If anybody that wants a landline number - Auckland is 09, Wellington 04, et cetera - those fixed geographic numbers come with voice over internet," Baird says.

He says the main change with VOIP is what happens when the power goes out or during a natural disaster.

"Fibre optics doesn't actually carry electricity through it. Whereas copper used to carry electricity. So the biggest difference is going to be if you want to have your voice over internet protocol running when the power is switched off you need to have some form of battery backup."

However, the Commerce Commission is taking One NZ to court, alleging a failure to "inform and protect" vulnerable customers by ensuring they're told how to call 111 during a power cut.

Telecommunications Commissioner Tristan Gilbertson says a number of New Zealanders still rely on landlines and have no alternative if they stop working.

"There are 684 of them who are vulnerable for the purposes of the code. These are the people whose lives are most at risk in an emergency situation because of health, safety or disability reasons," he tells RNZ.

During Cyclone Gabrielle last February, communication was cut off across Tai Rāwhiti, when landslips took out fibre optic cables and cell towers lost power.

In a statement, One NZ says they are "disappointed to learn of this, and have fully co-operated with the Commission since becoming aware of its concerns, and had been transparent throughout".

One company that has felt the move away from landlines is Yellow, commonly known as the Yellow Pages.

Despite being much smaller these days, with a combination of personal and business numbers and websites the yellow book is still delivered to 1.6 million homes across New Zealand.

Country manager Rob Jane has been with Yellow for 17 years.

"When I first started, businesses were putting fax numbers in nice, big, bold type in the book. Well, fax numbers have pretty much disappeared out of the book at a greater rate than landlines have dropped off.

"We're seeing businesses now promote their websites, putting an email address. And in more recent times they're putting a QR code in their ads."

Jane says around 380,000 residential phone numbers are still listed with Yellow, down 37 per cent from 15 years ago.

"We've seen over the years, there's always been a discussion around the books... I guess younger people in cities [ask] why do we need it? Then you'll see comments come in from older demographics outside the main cities going, 'Not everybody's connected to the internet, not everybody's online'."

Baird says it has been 30 years since mobile services were launched in New Zealand.

"In 30 years we've gone from 100 percent of homes potentially having a copper service to 100 per cent of homes having more than one mobile device."

New Zealanders will have to wait another eight years for 6G to be available, around 2032, he says.

-RNZ.