Once you arrive in Oz, purchase a SIM card. It should have the new phone number listed on it. IF not, then plug it in, and note the new number on your phone. Easy to see with this little Samsung app
* Phone INFO ★Samsung★ - Android Apps on Google Play
Once you know the new phone number, put the original Sprint SIM back in the phone. Call up your home number and enter the new call forwarding number. If that don't work from Oz, see if you can do it from the Sprint website, worst case, get a hold of Sprint tech support and have them do it. ( I can just imagine being oh hold for 30 minutes from Oz though )
But, you REALLY NEED TO THINK THAT ONE THRU....
do you really want anyone, and everyone, calling you in Oz and YOU PICKING UP THE TAB FOR THE CALL?
I think that it would be far better to SMS to only those who matter, what the new phone number is. In fact, it will show up on their phone with that new SMS you sent.
While you are "in country", do they really need to talk to you? I should think a simple SMS with nearly everyone should suffice.