It would appear that the purpose of the landline—especially one with a number still listed in the phonebook—is to answer robo-calls

Keywords: {0}

We “old folks” pay too much for this basic lifeline, considering the kind of abuse it gets from robo-callers who never add our names to the Do Not Call list, despite their promises. But we still think it is worth it to be able to call out in an emergency.

https://crazy956quilt.wordpress.com/2020/11/18/landlines-and-robo-callers