I bought my current phone answering machine 25 or 30 years ago. It’s still working. So I also use it for answering my landline. It seems to work because almost all the calls I receive on it are immediate disconnects when the answering machine goes off.

I still have a landline for a couple of reasons.

First, I live next to a heavily traveled commuting road. Which means that the cell towers are pretty much over capacity during morning and evening commute.

Second, iirc 911 is still not as informative on callers location for a cell phone as it is on a land line.

Third, yes, it is an artifact from when landlines were powered remotely and operated during power outages.

Fourth, I have had the land line number for 30 years and many people still have that as my contact number. Some of them, even, I still want to talk to. :)

But yes, at some point, I will probably close out the land line and reroute the number to my cell service or eliminate it.