The Comunications Fraud Control Association (CFCA) publised a link to a bulletin from the Department of Homeland Security (DHS) NCCIC. The bulletin describes threats and TDoS attacks against 911 emergency services. Apparently the attacker targets an administrative Public Safety Answering Point (PSAP) demanding payment. If the payment is not made, the attacker floods the target PSAP (911) with TDoS calls. The bulletin describes many calls, for an extended period of time, that affect both incoming and outgoing calls. The 911 service is likely targeted due to the high criticality of the service.
This threat and attack can be easily extended to contact centers, other government services, or any critical voice service for an enterprise.
Here is a link to the bulletin: