Looks like the 911 system is going national with an IP based 'solution'. They recognize this leaves them more vulnerable to cyber attacks. But hey, they reason, that already happens.

Many services have been now restored after reports that lines went down for call centres across Nevada, Nebraska, South Dakota and Texas. Federal officials have previously warned that the move to digital systems by emergency services has brought with it the risk of cyber-attacks. https://www.bbc.com/news/world-us-canada-68844879

Next Generation 911 (commonly referred to as NG911) is a digital, internet protocol (IP)-based system that will replace the analog 911 infrastructure that’s been in place for decades. https://www.911.gov/issues/ng911/

I'm not sure how old this article is:

The 911 System Is Not, Technically, National - While the overall 911 system has become an important part of the United States’ emergency preparedness, identification, and response, it’s not a national system. There are over 5,700 primary and secondary Public Safety Answering Points (PSAPs) in the U.S. that handle 911 calls.2 There are also over 3,000 counties that have their own 911 call centers. Each PSAP and each county is tied in to its own system and only handles calls from its designated area. https://www.waldenu.edu/online-masters-programs/ms-in-criminal-justice/resource/ten-things-you-might-not-know-about-the-united-states-911-emergency-telephone-number

NG911 systems, which operate on an Internet Protocol (IP) platform, enable interconnection among a wide range of public and private networks, such as wireless networks, the Internet, and regular phone networks.

911 centers are often targeted by malicious actors seeking to disrupt 911 operations and their ability to provide live-saving and critical emergency services to the public. These resources provide information on common attack vectors to 911 systems and best practices to mitigate cyber threats, such as ransomware, telephony denial-of-service (TDoS), and malware attacks. https://www.cisa.gov/safecom/transition-next-generation-911