This sort of mirrors how we do things at PagerDuty. Phone may be more reliable than SMS, but every telephony/messaging gateway fails sometimes. We use something like a dozen different phone/SMS gateways to prevent single points of failure, and do end-to-end testing of our SMS providers to check their uptime and latency.
Responders can customize their notification methods (push, SMS, phone, and email) and rules, so you can do things like get a lightweight push notification when an alert happens, and then a phone call 2 minutes later if you haven't acknowledged the incident. Teams get escalation timeouts that forward alerts up the chain if the primary hasn't responded after a period of time.
Responders can customize their notification methods (push, SMS, phone, and email) and rules, so you can do things like get a lightweight push notification when an alert happens, and then a phone call 2 minutes later if you haven't acknowledged the incident. Teams get escalation timeouts that forward alerts up the chain if the primary hasn't responded after a period of time.