Re: "to connect back to its old socket and power the home PSTN network"
REN is important only to make analog phones ring. Most recent phones with electronic ringer uses far less than one REN. Phones that are also plugged to the mains like DECT bases and faxes use that power to work, and of course portable devices ring from their batteries.
The REN number thereby just tell how many phones you can connect and have still them ring correctly. People still liking their electro-mechanical sets may need to look for a proper ATA or replace them.
If Aunt Gerty still likes her fax to exchange her recipes, or it's Oldsons & C., they still work over VoIP with the proper codec or protocols like T.38 but that has nothing to do with REN.
Biting the hand that feeds IT
