This reads to me as "I'm never woken up by phone calls from customers (or managers angry that customers are complaining about it being broken), because our aler

This reads to me as "I'm never woken up by phone calls from customers (or managers angry that customers are complaining about it being broken), because our alerts will wake me up first". If the phone rings, you answer it. If, after some assessment, it can wait until morning, you leave it til morning. Then you make sure it won't wake the next person up while they are on call.