Just in case your not aware if you want to make cheap international calls on Telecoms network, not using a calling card, there’s an option to 00.
If you dial 0161 then country code you will find the rates very cheap. Eg if you were phoning UK and previously dialing 0044xxxxx you would dial 016144xxxxx
This is a telecom service that isn’t publicised but details can be found at below link on telecoms website. It also has a calculator so you can look up the per minute rate.
Calls are billed on your telecom account as normal.
http://www.telecom.co.nz/0161