Not an Australian number, but from Tonga. A simple scam where automated calls are made globally. It rings briefly, or hangs up if someone answers quickly. Those who are curious enough to call back get charged for a premium call service. So if they don't leave a message and you don't know the number, don't call back.

Unknown caller. I let it ring out.

They've tried calling me twice already today and they hang up as soon as I go to answer. Yeah no not calling back to Tonga

Unknown number calling from tonga. Definite scam.