A mobile phone isn't an option either... trust me, i've tried that with her.
I do see her point, that she just wants a landline. No fancy internet, hub, tv package, etc, just a phone line. It's not much to ask, is it.
But as to why BT have sent her a hub, for her just wanting that, I can only assume there's been some misunderstanding along the way.
And this day n age everyone is trying to save on everything, I get that. £20 per year might not seem like much to you and me, but she's on her pension and £20 to her means food for a week or two. 'Same river, different depths' etc.
PSTN (Public Switched Telephone Network), a very old term but still used. That relies on equipment in the exchange which is being ceased. No new connection are being provided.
The replacement is VOIP (Voice Over IP), which means that calls are carried over the IP (Internet Protocol) network which does not have to carry any Internet connections.
So in her case, as a new customer, the hub is needed, as it converts the VOIP back to a normal phone connection, with that connection appearing on the back of the hub.
Without the hub, plugging a phone into the wall socket will result in nothing, not even a line indication. There is no alternative.
Not many providers offer a ‘landline ’ phone service without broadband, so if she is moving to BT , who was she with previously ?, TBH , it’s irrelevant now , but they should have stayed with whoever they were with if this change of technology is unwanted , it would only be temporary though , until December 2025.
After the 5th of September 2023 there wasn’t any longer the option to have a old style telephone only service from BT ( or anyone else using WLR ) so any phone service from BT effectively uses BT broadband, the customer may not want it , may not realise its the technology behind the phone service, but as there is no difference in price between this new way of providing telephone only and the old way , it’s pretty irrelevant.
Apart from the ‘router’ is mains powered, and the landline phone instrument plugs into the router not the phone socket on the wall, it’s pretty much the same .
It is an interesting topic given there is universal service obligations and lots of people may not want a broadband connection nor have any mobile signal (many areas don't have good mobile signal). When I in London am moved to digital voice in late 2023 for my telephone only line which has been with BT for at least 25 years (no switching) I think BT will be sending some kind of basic hug into which I will plug the corded phone rather than a hub 2.