IMPORTING A LUMIA 920 FROM THE US INTO AUSTRALIA

Hey guys this is my first post on the verge. I was wondering if I buy a Lumia 920 off contract from at&t will the phone be unlocked? I know about that it will technically work but Will I be able to put my Australian sim in it and it not be locked by at&t? The reason I ask is because the 920 cost $450 from at&t Or $800+ hear in Australia, so I think the trouble of importing it is worth it