We have FTTP now. We do still have a landline, but it is VOIP. When I made the order, I was told I could have FTTP and a copper line, but when the guy came, I got VOIP.
The disadvantages?
If the power goes down, so does the dog.
You have to dial the STD, even for numbers in your area.
Advantages?
Crystal clear line.
And two "lines": if one call is in progress and another comes in, you can pick it up. Similarly you can make a call if someone is already on one.
There is of course the issue of power outages and I'm thinking of a UPS. All the FTTP gear and the router are in the same location. So if that gets plugged into a UPS, it will stay online. And we can have a plug in phone which attaches to the router.
But back to the redundant phone lines: at one time, we had three lines, two business and a Dom line. So there's lots of NTE boxes, extension sockets and junction boxes all round the house.
I have used my plug-in line tester and all 3 lines are as dead as a dodo.
I've had to take two off the wall for replastering and decorating and I will take 3 more off later when work starts in those rooms. The rest are in rooms we are not working in.