South Australia is opening its State borders, but only to WA, NT and Tasmania, from 17th June 2020.
Restrictions on travel will still apply to NSW, ACT and Victoria.
Restrictions on Queensland appear to be under discussion at the moment.
The main effect of the change is that people entering South Australia from those jurisdictions will not be required to do the 14 days of self-isolation/quarantine.
However, if the other states do not bring in a similar change, anyone entering those states will still have to undergo any quarantine, or return exemption requirements that they impose.
For example, a day trip from WA to SA could still result in a 14 day self-isolation period on the return home.