Voice over Internet Protocol (VoIP) phone service cannot automatically detect where you are, because you could be calling from anywhere on the Internet. There is no single set of wires that carries your calls, so there’s no way to trace it to your location. In order to provide 911 location service, VoIP companies must tell their customers to register their locations, and then collect that information and forward it to E911 agencies. This article mentions that Vonage has succeeded in registering 94% of its customers’ locations, which is pretty darned good. Just goes to show that when industry is motivated by regulatory requirements and oversight, it can move quickly and efficiently.
Stephen Seitz Honored by E9-1-1 Institute - Government Technology