A little birdy tells me that NZ Comms are deploying both 900 GSM and 2100 3G networks - they aren't just driving around in the GSM Lada that we have all been joking about. In areas where they are live it's certainly only the 900 GSM network that is visible with a network scan.
Their BTS cabinets are big enough for gear for both networks and their panels (they are only using one standard model) are apparently dual band and interesingly looking at one of their new Wgtn sites this morning (that only went up a week or two ago) it's possible to see 4 cables from the bottom which potentially indicates dual 900 and 2100 TX/RX.