2degrees customers in Auckland with newer smartphones, tablets or data sticks may notice faster download and upload speeds from today.
The company switched on its first 4G services from 72 cell sites in the central city.
Chief executive Stewart Sherriff said the company would triple its 4G footprint in Auckland and launch 4G in Christchurch, Wellington and Hamilton by the end of the year, with a roll-out to "provincial areas" next year.
The maximum download speed people might experience was 150 megabits per second, which the company said was about 10 times faster than standard 3G connections.
However, speeds would depend in part on whether other customers were connected to the same segment of the cell site at the same time.
Vodafone and Telecom launched their first 4G services last year. Vodafone said it now provided it in 38 areas, where about half the population lived or worked. Telecom offers 4G in Auckland, Wellington and Christchurch and some other parts of the upper North Island. None of the three carriers charges a premium for 4G.