Landline use, or fixed-access lines used only for voice calls, continued to decline.
The number of connections in homes fell by nearly a quarter in just three years to just under 200,000 last year.
Average mobile calling in New Zealand reached 118 minutes per connection per month.
This was 33 minutes less than people in Britain, who talked for an average of 151 minutes a month per subscriber.
A sharp rise in the tally of cellphone calls since 2015 was a reflection of the "buckets" of minutes now being offered to customers on all mobile networks, said telecommunications commissioner Stephen Gale.
"Mobile companies have thrown in more minutes in their mobile packages and people have slowly got used to the idea that calling on a mobile phone isn't risky or expensive," he said.
"Mobile is clearly catching up now everyone realises it's part of their package."
Last year was the first where more minutes were spent on mobiles than on landlines, with people talking on fixed lines for a combined total of 6.7 billion minutes.
The number of fixed lines has hovered around the 1.8 million mark since 2006, thanks in part to people and businesses using a fixed line for broadband connection.
Though landline uptake was low, people held on to their existing landlines for a long time, Gale said.
Often this was so older family members were able to get in touch, which would not be so common in future.
"Stand-alone voice services will become very rare," Gale said, although when asked how quickly that would happen he said it was difficult to predict.
Spark had seen a "significant" drop in the number of customers who had landlines, a spokeswoman said.
Only a minority who had a fixed line for broadband opted to have a voice line as well.
"Instead most new customers opt for a "naked" plan, which gives them broadband data, and then they use their mobiles (or "over-the-top" applications like Whatsapp or Viber) for calling," she said.
Vodafone has been approached for comment but did not respond by deadline.
