Because VoIP services use IP networks rather than landline or cellular networks, VoIP E9-1-1 requires a different solution. VSPs must resolve a new set of challenges for determining the location of the caller, routing the call to the closest PSAP and automatically delivering the caller’s location and call back number to the PSAP.

The challenge of locating VoIP 9-1-1 is a consequence of VoIP's flexibility. Depending on their level of mobility, VoIP subscribers can be classified as static, nomadic or mobile. Static subscribers use VoIP as a landline supplement or replacement, typically using residential cable or DSL. Their VoIP phone is deployed in a fixed location and uses the standard North American Numbering Plan. LECs can support static VoIP subscribers with local telephone numbers in the same way they support their wireline subscribers: by provisioning each VoIP number into the ALI database so the selective routers can recognize and correctly route the 9-1-1 calls. But in most cases, this wireline model only supports static subscribers with local phone numbers. Because of the frequent use of non-local phone numbers, VSPs face challenges similar to those once faced by cellular carriers in terms of routing calls and location data through selective routers that don’t recognize numbers from outside their area.

Nomadic subscribers view VoIP as a highly portable telephony configuration that allows them to establish a telecommunication connection wherever they can obtain Internet access. Nomadic users take their VoIP service with them while on the go, connecting at the airport, in their hotels, and at any available hot spot.

Mobile subscribers not only take their VoIP phone with them wherever they go, but they remain continuously connected. Much like cellular technologies allow today, mobile VoIP subscribers will eventually be able to roam from their home-based telephony connection throughout a continuously interconnected Wireless Fidelity (WiFi) network. As coverage of WiFi hot spots and other wireless methods for WiFi access become ubiquitous, the number of mobile VoIP subscribers is expected to increase.

Because of the mobility of nomadic and mobile VoIP subscribers, VoIP 9-1-1 solutions are dependent upon all subscribers to accurately identify their location when they register for VoIP services, as well as every time they log in. However, since it often takes 24-48 hours for subscriber location data to be updated in the ALI database, new solutions are required for rapidly updating location data.