A suggestion regarding the issue of a change of plans mentioned by several posters. When notifying others (including AMSA if you have a PLB) of your trip itinerary before you depart, state clearly that the plan can be varied if conditions demand. List the alternative locations you may consider visiting instead. Its a big country, so they may be hundreds of kilometres away from your original location/s!
Note also, if you have not been aware of this change, Telstra phone boxes in country towns and in some remote places are free to use. For example, Balcanoona rangers HQ in Vulkathunha, and Arkaroola, both in SA.