Yes. Every time I've ever participated in an oncall rotation with 24/7 coverage, we absolutely did have one another's phone numbers, whether for work-issue phon

Yes. Every time I've ever participated in an oncall rotation with 24/7 coverage, we absolutely did have one another's phone numbers, whether for work-issue phones or - as in my own case, since I never have wanted to bother with a second phone - personal ones. Sure, not everyone had everyone else's number, but among all of us we had enough coverage to reach anyone who might be needed to help respond to a sufficiently severe incident. The point was to make sure that, even if all of our infra including third-party IP comms and chat providers was hard down, we'd still be able to talk to one another and figure out what to do about it. For an organization on Facebook's scale to overlook something so fundamental implies lots of things about the collective blind spots of its engineering and operational culture. None of those things make me less glad I so assiduously avoid even using any of its products, to say nothing of relying on them - at least to the extent that I'm able to avoid it, given their apparent ability to break half the anglophone Internet more or less at whim.