Spark customers in Auckland's Devonport and Wellington's Miramar still on old copper phone lines have to switch to newer technology by December 18 - or be faced with no service or of switching phone companies.
Technology Users Association head Craig Young told the Herald it was "a form of forced migration off copper".
But Spark was quick to point out that a majority of its customers have already left copper behind, making voice calls over UFB fibre or via fixed-wireless, which uses its mobile network as a landline substitute.
Making a voice call using one of the two newer technologies is functionally no different than over an old copper phone line - but with the key exception that a fixed-phone plugged into an old copper line will keep working during a power cut.
"The issue will be clearly explaining to those moving from a copper landline service that in the case of a power outage, they will no longer be able to make a 111 call using their replacement landline service," Young says.
"This tends to impact the elderly, who in some cases do not have a mobile phone service. So Spark will need to work with their customers to ensure they understand this situation."
The Commerce Commission is looking for a solution for emergency calls in the post-copper world, but is still in the early stages of its process.
Alarms, medical monitors also problems
Other potential problem areas are home or medical alarms designed to work with copper line technology.
A Spark spokeswoman responded: "A range of devices might be affected. We have a dedicated customer care team to work through individually with customers.
"We intend to take extra special care assisting those with medical and security alarms or any type of special handset that supports disabilities to ensure their equipment is compatible with wireless or fibre landline services.
"Spark has tested a number of special devices to check that they work on the wireless network, although there may be many others we are not aware of. For this reason, we won't be moving customers with any type of special device across until we can make sure there is a wholly appropriate solution available."
Spark customer director Grant McBeath says when Devonport and Miramar people move off copper line voice-calling, they will save money. All affected customers will be contacted at least 90 days before the December 18 deadline.
Any customers who want to leave Spark will not be charged a cancellation fee.
McBeath says the public switch telephone network (PSTN) technology used for copper line calling is now outdated. It was developed in the 1980s and hasn't been manufactured since 2003.
Nearly half of households mobile-only for calls
A Commerce Commission report released in March said 1.6 million premises nationwide were within reach of UFB fibre. Of those, 880,000 (or 55 per cent) had connected.
The regulator said a further 188,000 homes or businesses were on fixed-wireless connections.
Copper connections continued to fall, but about 581,000 homes or businesses were on the older technology, the ComCom said.
he commission also said that 46 per cent of households are mobile-only, having jettisoned a landline.
Copper on the way out for everyone
Although Spark has gone on the front foot with Devonport and Miramar trials, voice calling over old copper lines is to disappear in large parts of the country - whichever phone company you're with - over the next few years.
An update to the Telecommunications Act, which will be phased in by mid-2022, allows UFB fibre network operators - easily the largest of which is Chorus - to cease offering copper service in areas where UFB fibre is available. By 2022, that will be more than 80 per cent of the country.
That could mean physically ripping out copper from the ground, or down from wires, or simply switching off PSTN hardware.
It's an acknowledgement by politicians and regulators that it would not be economic for Chorus - and Enable in Christchurch, NortPower Fibre in Whangarei and UFF in the central North Island - to keep maintaining increasingly creaky copper in the fibre area.
Rivals aren't taking the same copper-or-bust-by-December approach as Spark. Vodafone says it has no set timeframe or plans to retire landline copper voice services, for example, even though customers are turning to alternatives at a brisk pace. But the above-mentioned regulatory changes mean copper is headed for the dustbin of history regardless.
Pros and cons for Chorus
For Chorus, a Spark (or Vodafone or Vocus or other ISP) customer upgrading from copper to UFB fibre is a good result. On most plans, it gets a clip of the ticket that equates to more than half the monthly cost of the broadband plan.
With fixed-wireless, however, Chorus gets cut out of the loop - physically and financially, as Vodafone, Spark (and in rural areas, 2degrees) use their mobile networks to deliver broadband into a home or business, where it's shared between devices using a Wi-fi router.
Spark has been on a heavy drive for several years to get more customers onto higher-profit fixed-wireless plans. At its most recent financial briefing, it said it now has 142,000 customers (of around 699,000 total) on fixed-wireless - a shift that has moved about $70 million in revenue a year from Chorus' pocket to Spark's.
And under its new 50 per cent Infratil ownership, Vodafone NZ has made fixed-wireless a priority. Chief executive Jason Paris wants a quarter of his company's 420,000-odd fixed-broadband customers on wireless plans in two to three years.
Fixed-wireless broadband has been traditionally cheaper than UFB fibre but also subject to tighter data caps, prone to congestion at peak times and not suitable for the most intensive online tasks.
However, Spark and Vodafone's respective 5G mobile network upgrades will allow faster fixed-wireless service and more unlimited data plans. Spark launched its first 5G service in a series of small South Island towns late last year, and Vodafone plans a broader fixed-wireless 5G service this year.
Already, Spark and Vodafone have significantly raised their data limits for fixed-wireless over 4G, and Vodafone is trialling several thousand fixed-wireless customers on unlimited data fixed-wireless plans.