WOW, I thought I was the only one managing this antique.
We have a 24/48 Vantage, that won't stop working. Have thought about pouring oil over it, but owner would probably blame me. Did have a little smoke rising one time, but I was foolish enough to pull the plug, instead of letting it break into a full fire.
Anycase, I do have a source for parts and refurbed phones on this beast. Instuctions are available as well.
How many telco lines do they have now? Haven't worked with a 12, what's it capacity? If it needs parts, the cards are pretty cheap, about $100 each. If it's like a 24/48, you may need two cards.
I am sure my source would be able to upgrade to a 24/48, if they really wanted to, and supply any parts for the 12. I do not have a financial interest or stake in the company.
Hmmm, make sure you have the battery switch on, before you disconnect the power. Probably is already on, otherwise they would be talking about reprogramming the beast with every power outage.
Good luck,
Jeff