5G wireless technology is hyped as life-changing, connecting everything from cars, fridges, robots and people in real-time.
Spark and Vodafone already offer limited coverage, and this year will ramp it up.
But anti-5G protestors claim the roll-out means humans are being used as scientific guinea pigs.
So what is 5G?
The promise from Spark and Vodafone is that it's all about speed, and we don't even know what its potential is.
Vodafone was the first to launch 5G, with limited coverage in Auckland, Wellington, Christchurch and Queenstown.
Spark decided to go rural, with 5G wireless broadband in six South Island towns.
The race is on to see who can roll out 5G the fastest.
"Our 5G programme - we have rolled out 130 cell sites to date, we will have 400 cell sites rolled out by the end of this year," Vodafone head of technology Tony Baird told Newshub.
Vodafone isn't building new towers, but is instead refitting existing 4G cell towers with 5G antenna, which are smaller.
"Two of these (5G antenna) equal one of these existing 4G antennas."
And the 5G antennae are far smarter.
Current 4G cell-sites are always on, blanketing the area with radiofrequency radiation.
5G transmitters will initially use similar 3.5gHz frequency, but the difference is that it's targeted.
Beam-forming technology means the signal switches on when a device connects to the transmitter - and it means downloads can be up to 10-times faster.
But does it mean more exposure to radiofrequency radiation?
Spark operates a 5G lab to showcase its possible uses.
"We have tested robustly inside and outside, and the results show the emissions are virtually identical to 4G," Spark 5G innovation lead Michelle Baguley told Newshub.
The top radiofrequency radiation absorption rate internationally is set at two watts per kilogram averaged over a person's body.
New Zealand exposure levels are set at 50-times lower than that.
And measurements at cell-sites show most levels are less than 1 percent of that lower limit. But this is where the arguments start.
Stop 5G movement member Michael Baughan told Newshub those standards were set 20 years ago and are under review.
"There's plenty of evidence that existing frequencies can be harmful, continuous exposure. Plenty of studies, thousands of studies that are currently being ignored," he said.
The Prime Minister's chief science advisor Professor Juliet Gerrard has recently looked into whether radiofrequency radiation causes harm.
"There is the odd study that shows a correlation, but they are far outweighed by clear consensus there isn't reason to be concerned," she said.
She believes people also get confused, because radiofrequency radiation is classified as a "possible" human carcinogen.
Out of five levels, that puts radiofrequency radiation in the same category as pickles and dry cleaning. However, that is being reviewed this year.
"Possibly carcinogenic means we can't rule it out, but it is a very low risk," Professor Gerrard said.
A risk that's acceptable to health authorities and phone companies - but not everyone believes in the future of 5G.