The 911 emergency number was created back in the day when telephones were connected by wires, before cellphones or VoIP (Voice over Internet Protocol) in the home, and before Multi-Line Telephone Systems (MLTS) in the enterprise.
In the early days, anyone could dial 911 for police, fire or medical emergencies. However, in 2017, dialing 911 unfortunately is no guarantee that a call for help will reach a 911 service that can identify the location of the caller immediately. As a matter of fact, when consumers dropped land lines and started using Internet phone services like Vonage, a 911 problem surfaced.
A Vonage phone was hooked up to the Internet, and no physical location was connected. So after litigation Vonage (and other competing services) changed the requirements to use the service, obligating customers to register their physical addresses. MLTS raised a different, but equally problematic, issue.