Hoibbycat*, my landline phones have a speaker button, always use these when on the phone as my hearing is not very good. So ,makes little difference if I am using landline or my mobile in that regard.
I have NEVER had any security number sent to my landline, always to my mobile/laptop.
'Bluebelle*, surely if you had no electricity then the landline would not work. Prior to fibre, I always kept a spare simple handset for landline, which I could just plug directly in as a phone without any electricity to use in such an emergency. Now I have fibre that little phone is going to Charity Shop.
I do keep a small power pack, always charged up, so in the event of even quite a long outage, I could use that to charge my mobile.
It appears (at the moment) that it is not meaning any extra payment to keep my landline - have handset in living room, bedroom and kitchen - so always nearby. It does have a answerphone, which I always forget to listen to messages and encourage people to use my mobile phone mainly.