For those who might not know, ISDN was the first digital subscriber technology. Telstra ended the residential-grade service years ago. Now, businesses will need to look into changing over.
It was a fairly neat solution in the days of 56k modems - 128k on a BRI with DoV on the likes of a Cisco 1003 - left the connection running continuously … and worked well in a semi-rural environment as well …
It is very easy to say upgrade your PABX, but not so easy to do due to the cost. ISDN required special digital hand sets (four wire rather than two I seem to remember). So likely not only the PABX, but all the hardware associated with it.
ISDN is still being used by small businesses who may not hard pressed to come up with the sort of money required to get a new PABX and phones etc in this time of ‘retail recession’.