Australia uses a prefix number to represent each state and territory.  Most numbers apply to broadcast and ham call signs with the exception of ACT hams.

0 = Antarctica

9 = Australian external territories

8 = Northern Territory

7 = Tasmania

6 = Western Australia

5 = South Australia

4 = Queensland

3 = Victoria

2 = New South Wales and the Australian Capital Territory (ACT, Canberra).

1 = Australian Capital territory (ACT, Canberra) - ham licences only eg VK1xxx.

As for the letters of the broadcast call signs; some refer to the operators and some have historical interest.

A few examples;

5DN is a South Australian call sign; the DN refers to Denise and Norman who were a brother and sister who operated a pioneering broadcast station from their flat for half an hour each week when broadcasting was truly new.

2SM is a Sydney New South Wales call sign; the SM stands for Saint Mary's and refers to the catholic cathedral in Sydney which owned the radio station.

5AD refers to the "Advertiser" newspaper that owned the station.

Some letters refer to the geographic location of the station.

Examples;

5PI is Port Pirie, South Australia.

5SE is Mount Gambier which is in the South East of South Australia.

2QN is Deniliquin, New South Wales.

7HT is Hobart, Tasmania

Other call signs baffle me as to their origins; eg  3UZ (Victoria), 4KQ (Queensland).  Somewhere there must be a radio historian who can put it all together.

 

Some details here; https://en.wikipedia.org/wiki/List_of_radio_stations_in_Australia