I found a website that lists the frequencies for cellphone networks in NZ, and it said:

Telecom New Zealand Limited - 3G 850/2100
Vodafone Mobile NZ Limited - GSM 900/1800, 3G 2100
2degrees Mobile Limited - GSM 900/1800

But then in the text it also mentioned 2degrees have a 3G (WCDMA/HSPA+ 2100 Mhz) network. And Vodafone's 3G network requires UMTS 850 or UMTS 2100.

Finally Telecom use 850 Mhz , and in some major cities 2100 Mhz but it's for capacity only (?).

I work in a store where we sell 2degrees and Telecom phones, but people always ask will this work on Vodafone or Telecom or 2degrees, lol.

I got a Telecom branded cellphone to work on 2degrees today and was surprised.

I wonder, what UMTS is? But I guess 3G phones that work on 2degrees may not support 3G on Vodafone then.

And only phones that do WCDMA 850Mhz will run Telecom XT.

Would that be correct?

It seems often people won't be able to pxt or use internet when using a phone on a different network too.

Any thoughts / links / advice would be great. Thanks very much!