Corrections Act 2004, ss 113, 114; Prison Operations Manual, C.02.08
Yes, all calls are recorded, and they can be used as evidence in a criminal court case. As soon as you pick up the phone from the prison to ring out, there’s a recorded voice message on that phone telling you the call will be recorded.
The prison staff must not monitor (listen to or record) calls between you and:
your lawyer
the Ombudsman
prison inspectors
the Human Rights Commissioner
the Independent Police Conduct Authority
your local Member of Parliament (MP).
If your call is being monitored, prison staff must stop as soon as they realise that you are speaking with someone who is exempt from being monitored. The recording must be wiped.