Have we learned nothing? This is literally what happened a few years ago with the big Optus outage. They were doing a change overnight, and broke everything. But all the on-call technicians were asleep because nobody could call their Optus phones to wake them up. Couldn't even try to raise them with email pings because their home Internet was also Optus. Management were clueless, because nobody could call them either.

Everyone found out in the morning from the news or when they rocked up to work per usual and the place was an ants' nest.

Issue some people phones on a different carrier, for pity's sake.