I have just returned from The Land Downunder, and found a good SIM card deal.
The company is called Amaysim, and for $30 I got a SIM card that permitted 30GB of data …. but I never used that. The BEST part was that for 28 days I got unlimted talk/calls to any (standard) Australian and International numbers !
Worth a look … https://www.amaysim.com.au/plans/mobile-plans