Most of them comes from plans, and most of them are 24 month plan, except for Optus 12 months.

Optus (scroll to the bottom) - http://personal.optus.com.au/web/ocaportal...s&site=personal

Telstra (click on iPhone 3G Plans tab) - http://www.telstra.com.au/mobile/phones/iphone/pricing.html

Virgin Mobile - https://www.virginmobile.com.au/shop/p-396-...aign=ppc_iphone

Vodafone - http://store.vodafone.com.au/iphone/

Australia don't have those ah beng hand phone shops that sells cheap phones. Before buying, you might want to ask the seller if it's unlockable while within plan.

But basically, if you are not staying here for at least 12 months, it would be hard to get one