VoIP involves the transmission of voice data packets using Internet Protocol (IP). VoIP presents an attractive business model to service providers because it enables them to offer voice services at a fraction of the price of traditional wireline services and at the same time offer premium services at higher margins (e.g., video conferencing, multimedia messaging and unlimited call bridging). While many consumers are attracted by VoIP's inexpensive voice service, others appreciate VoIP for the additional flexibility and mobility it offers. For instance, a residential VoIP subscriber living in North Dakota might use a Florida phone number so his family in Florida can call him without incurring long distance charges. A businesswoman might subscribe to VoIP so she can take advantage of premium services while on the road.

But there is one major drawback to today’s VoIP services. In the absence of reliable 9-1-1 services, consumers may refuse to rely on VoIP as their primary phone service, and others may not adopt it at all. If VSPs fail to deliver comprehensive E9-1-1 services, the FCC may step in and mandate it. VSPs who want to avoid these business and regulatory risks must overcome a number of technical challenges set forth below. These challenges are best understood in the context of the wireline and cellular E9- 1-1 solutions in use today.