Can I use a UK unlocked iPhone in Australia?

I have an iPhone 4 locked to O2. I'm going to live in Australia for a year. If I get my iPhone unlocked will I be able to use an Australian SIM card to make calls when I'm there?

Ofcourse You can

Definitely!

Yes. You can use UK unlocked iPhone in Australia…

Yes of course you can, but in order to avoid excessive roaming costs you should consider using a local Australia sim (with a dual sim phone) or perhaps a travel sim card like MySims2Go (that's the one I use, but you can find a lot of similar companies)

Yes, you will be able to use it to any carrier.