Ok, so, Mum: "can you do this I don't know how" as she hands me a Spark branded 4g wifi router.

Of course, I only get half a disjointed story about it, and I'm not up with the play on the current situation.  Apparently she is "the last one on the street with a normal phone and Spark has told her she has to use this for her phone now it will be cheaper", this is in suburban Christchurch.  It's a 4g router, with a line port for the phone.

As far as she says has not signed up for any broadband plan, but I would not take that as gospel.

There are multiple phone jacks in the house, but *right now* she only uses one of them.

Is this kosher or has she been sold into something she shouldn't have been?  I remember vaguely the copper POTS network being discontinued, but I'd have expected that to wind up being spark or whoever running fibre and fitting a VOIP to the POTS demarcation point when the time comes so that all the phone sockets in the house "just work" and that would be part of "line maintenance"?

Is using multiple phones in a house not the done thing any more, I don't use phones myself so I really don't know what is common.