When I arrived at Auckland airport, there were a lot of telecom carriers you can choose, and the clerks promoted their products actively at the booth. Besides duty free, if you buy two sim cards, you can get 20%off.
However, I bought a Spark sim card in the store in the arrival hall. The monthly deal requires a minimum three month contract, and I chose the rate of NZD$39.99. There are 2 gigs(student visa plus 1 gig) with 300 minutes free talk time and unlimited texts for a month.
You can usually see the payphone on the sidewalk, there is one gig FREE-WIFI every day for you, especially, SPOTIFY for free in two years.
( Taiwanese people said that KKBOX doesn't work in NZ.)