With regards to these numbers coming and going, I had a poke around the ACMA register for SmartNumbers (this includes 1300) numbers. You can access it
here. After a bit of digging, here's what I came accross.
If we search up the old numbers such as 1300 659 115 or 1300 659 134, we can see these were originally allocated to Telstra (Qantas' old phone operator) and now belong to AAPT Limited (which is TPG,
who now handle phone services for Qantas). These numbers were allocated back in 1995, so I assume Qantas has owned these numbers for a while.
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However, things begin to get interesting if we look up one of the newer numbers, such as 1300 024 715. These were allocated directly to TPG (AAPT Limited), and were allocated very recently (4th of February).
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It would be logical to think that Qantas might have asked TPG to get a new block of 1300 numbers ready for these priority phone lines at the same time, and indeed this is the case. We can use the ACMA website to look up 1300 numbers allocated to AAPT Limited on the 04/02/2022...
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Hey, these look familiar! 1300 024 715 and 1300 025 390 are former numbers, and 1300 025 396 is the new (just activated) priority number, as mentioned above by redwoodw.
I've called the other 3 numbers and can confirm they all route to Qantas (but are not priority, since they ask for FF#)
Therefore I'm going to make an educated guess that if 1300 025 396 stops being a priority number, that the next number will be 1300 026 698, 1300 026 704, or 1300 020 873