The Netherlands has a network for the emergency services that is entirely separated from the normal phone network ("Noodnet"). It has a limited service and band

The Netherlands has a network for the emergency services that is entirely separated from the normal phone network ("Noodnet"). It has a limited service and bandwidth and normally has no interconnection with the normal phone network (so is not intended or usable for emergency calls from the public), but is designed to be very resilient. I don't think it is used when the normal phone network is still functioning. I have no idea how they test it; it must all be rather expensive.