Can you use unlocked iphones anywhere?

I'm thinking of buying a iPhone that's unlocked on E bay but I'm from New Zealand so does that mean i can put my Sim in it to use it still?

Yeh you can. I live in NZ but I bought my iPhone in Germany unlocked. It works fine on Telecom, Vodafone (NZ and AUS) and AT&T in the US.

Yes, unlock phone can work with whatever sim u put in it

Yes you can.

Yes as long as the carrier is on the same network type as your iPhone (GSM or CDMA)