Unlocked from Orange iPhone 4 won't detect new network sim

In December 2011 I paid Orange EE to unlock my iphone 4. I received the confirmation email with the instructions for itunes and it unlocked. I then used the phone in Australia with a pay as you go sim with no problems at all. Now, a year on and many updates later (to itunes 11 and iphone ios 6.0.1) I want to use my phone in NZ. However, itunes doesn't show a space for the phone number, just the imei number and the phone just says no service. But whatsapp has detected the new sim so I can't figure out what to do next! I've done a restore with the new sim in hoping that would fix it but still nothing. Has anyone else had this issue and managed to get past it!?