This will all revolve around the definition of the service you have. Is it
1) The ability to make voice calls on a phone, or DECT base station plugged into a single master socket.
2) As. above, but for multiple sockets distributed around the property.
3) 1 or 2 in the event of a widespread power failure.
4) The continued operation of a Telecare or burglar alarm system dependent on power from the copper line.
The current copper service to the majority of premises encompasses all of the above and these are the services apart from option 2 which is a personal option.
I do not see why any customer should have to pay for replacement equipment simply to return them to a working phone service.