and landline won't? it's also oversubscribed. pretty sure it isn't guaranteed e2e circuit switched either, and that it hasn't been for quite a while.

In the US the POTS telcos have a strict availability requirement that constrains the oversubscriber ratio. It was these requirements that lead to the development of the erlang unit in queueing theory.

So don’t worry about that particular issue on the POTS side. On wireless, it feels like anything goes (not really true, but by comparison it’s the Wild West)