As of October 2022, telcos aren't required to maintain their copper infrastructure. This is partially why some areas are seeing $100 per month POTS lines (they want you to leave! LOL). To get an endpoint license, Avaya will first require you to upgrade to 11.x. That license pair will likely run you over $1000. My recommendation is to look into a Kings III dialer or similar box. They're maybe 5" x 5" with a small antenna on top to talk to the 4G network. At the bottom of the box is an analog phone jack. Most mobile providers consider this an IOT device and probably won't charge more than $30/month for the service. I've been putting these in elevators and other such things. Most modern alarm panels have a cellular module as well. You might want to look into those options rather than trying to have the dial tone hosted from your IPO.
Tim Alberstein