Considering that in North America, two carriers can share the 850 MHz band in a given market and have sufficient spectrum (topped up with a little in urban areas at 1900 MHz), it seems crazy that that wouldn't be possible in New Zealand.
Still, good news for New Zealanders, and for foreigners who will visit there.
CA: SaskTel, Wind postpaid; Rogers, Bell postpaid iPad flex plans; US: T-Mobile postpaid data, prepaid voice; PureTalk (AT&T MVNO) prepaid voice/data; AT&T prepaid iPad plan
Hardware: Too much but notably iPhone 5, iPad Mini Retina LTE, Moto G LTE (N.A. version), iPhone 4. All unlocked.