E911 for emergency calls and VoIP have had a love/hate relatiobship for many years, but as Intenet based calling becomes more and more the norm, and as LTE will bring IP based calling (i.e. VoIP) to the mobile world for real, E911 and the problems associated with it will come to the forefront more and more.
Today's Government Technology piece on the subject provides good background and helps build the case for more migration to IP based E911. In my view the PSAP technology has to go IP. When that happens, expect Skype to become E911 capable.