We use a reverse geocoding service. The goal is to provide an address that is close to you (within 50 or so metres) which is better than the alternative of what responders currently get when you call and do not know your location.

Within the app itself you can move the pin (a la Uber/Lyft style to update the address) you want to send.

Here is a bit on the current status of Wireless Enhanced 911

http://en.wikipedia.org/wiki/E911#Wireless_enhanced_911

Cellular phones can use several technologies that can assist in providing and X,Y coordinate of the device. These can be extremely accurate, depending on the data available. Look on Wiki for 'SkyHook'. This information is NOT available to 911 on phone calls, nor dopes a data channel exist to even transmit the data from the device to the 911 center. This is why the App is useful, but the App, needs to talk to something on the 911 center side. Without that piece, there is no way to get the information from point A to point B.

Fletch, that's spot on. This is why the utility is gated to the areas where text to 911 is available (in upcoming update) and why 911 will send you a bounceback if the dispatchers aren't so equipped