I really think Telecom would be stupid to sell a 3G only device considering they are launching their 4G network later this year.
From what I have read 2 months back. Telecom did show me a specs sheet detailing that it is 4G compatible. However, they may have changed their minds. Fingers crossed they aren't that short sighted.
From what I can tell, the hardware will be exactly the same for all Australasian carriers.
The difference may be the firmware.
TNZ 4G is still about 6 months away, so it's a fair while to wait.
If they're crippling the firmware for the meanwhile I guess you could flash it - or test out the dual-carrier capability.
I have to say - you've done pretty well with that Easter deal.