How do I use iPhone4 in Korea that I bought in NZ?

Hello.

Its urgent.

I have used iPhone4 in NZ for a while and I came to Korea and got to use iPhone here with Korean Sim Card but it does not work with it.

They asked me to contact Vodafone NZ and Apple Customer Service bout country lock.

Could you guys please let the phone use in Korea for around 2 months?

I need to use it asap.

Kind Regards