I received a call from this number today. I rang back and got a message saying it was Mondial calling on behalf of a charitable organisation (they didn't say which one). It seems legit enough... but I wish charities wouldn't call using strange-looking numbers! My immediate reaction is that they're someone sus.

Got a call from this number just now.  My answerphone always picks up, but they never leave a message.  When they are gone, I do my number recall thing (*69# on Optus) and retrieve the number.  It was (02) 8001 3403.