Thanks Tim, I have a linksys ATA SPA3102 with exetel on line1 amd Pennytel in the gateway. Even with the changes you've suggested I still get that blessed engaged tone when making calls and end up getting charged when the person on the other end answers
but no conversation can come about.
According to the manual, the linksys devices (or some linksys devices) generating a local “fast busy” (re-order) tone when they decide that the dialled sequence is invalid.
So by differentiating between the re-order signal, and a busy signal, you can tell if the problem is with your ata, or elsewhere in the network.
The fact that the call is going through is rather strongly suggesting to me that you have an ata generated reorder signal, and that the call is therefore being dropped by your ata.
So this then is the place to start looking.
This being said, it does not answer why this is now an issue.
I will always be deeply suspicious of the ultimate controller of the australian telco infrastructure. My suspicions are based on Telstra's track record. They do not attract customers by choice, they aim to conquer.
You may need to adjust your ata settings so as to compensate for changes in the pstn.