jjnz1: 2Talk has an excellent set features like Remote dial tone, which you can use in conjunction with Vodafone's NZ Best Mate and an Android program like Prefixer.
This will allow you to make a dial plan on your android which specifies that all landline etc calls go through 2talk, making them free. Call quality is still perfect, and not subject to VOIP 3G errors because its a normal GSM call.
As far as I'm aware, no other NZ ITSP offer such services?
Xnet VFX has the same function. Look under Remote Office in the following document: