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