At AWS, it isn't uncommon to get paged via email, SMS, phone-call, and a smartphone app in addition to having an actual paging device (usually a dumb phone) separate from one's personal phone or laptop to avoid cases where the personal phone and email are both down (I believe this has happened, and not just once) and that someone important is out of reach in a time of dire need.

Source: ex-AWS.

Indeed. Uptime and (maybe less relevant these days) better reception in hard-to-reach places.

Plus there are often (or at least used to be) regional paging companies; it’s nice to deal with a service provider who’s local and small enough to care about your business.

One unlikely downside: I recall a very localized outage years ago that apparently no one at the paging company noticed and there weren’t enough users in the area to complain before it bit us.