The articles I've found on Computerworld New Zealand discuss about the relationship between TelstraClear and Vodafone, which is the current carrier of all GSM traffic.

Ericsson, Nokia, Nortel Networks and Siemens were shortlisted after a pre-tender information-gathering exercise and will be issued with more requirements of the network soon.

TelstraClear presently resells Vodafone's mobile services to its customers, but chief executive Rosemary Howard says in a statement that the arrangement "doesn't give TelstraClear the control we need".

According to New Zealand rules a mobile operator who has a network covering 10% of the country to roam on another provider's network. And this is the point. If TelstraClear covers the Auckland region with 3G, users in other areas will have access to its services - over GSM only, roaming on Vodafone.