Android: Select Apps > Select Telco Services/TelecomNZ/SIM Toolkit > Select Roaming Menu > Select Manual > Select Sponsor (local network) or TNZ > Select Accept  (Depending on version of SIM card and OS the name of the second step will vary)
iPhone: Select Settings > Select Phone > Select SIM Application > Select Roaming Menu > Select Manual > Select Sponsor (local network) or TNZ > Select Accept
iPad: Select Settings > Select Mobile Data > Select SIM Application > Select Roaming Menu > Select Manual > Select Sponsor (local network) or TNZ > Select Accept
Nokia with Windows Mobile: Select: Settings > SIM Application > Show Applications > Roaming Menu > Manual > Sponsor (Local networks) or TNZ