Speaking on Deep Background, the Press Secretary whispered:
When somebody in the office picks up a phone and dials EXTERNAL-911 how
do the emergancy services know they are in one building rather than another
office across town?
The PBX intercepts the call and uses special trunks to the PSAP;
it also has to send data telling where the caller is.
Here's one vendor: http://www.tonecommander.com/e911/How%20PBX%20ANI-LINK%20Works.htm
I think this scheme isn't going to work for VOIP. It relies on sending an
ANI ID code which is setup in the E911 database with a more exact address.
This is fine for a PBX with fixed phones. But it won't work for VOIP
phones that could be anywhere now and somewhere else in 10 minutes, just
by plugging them in to a new jack (and don't forget wifi phones).
I think that VOIP phones will either ultimately be exempted, or required
to have GPS (or triangulation or some other scheme), and the ability to
send the GPS data to 911 services like cellphones. (And GPS doesn't work
so well inside buildings, so I sort of doubt that its going to be very
good as a locator for VOIP phones). I think that this is going to be a
hard problem to solve.
Or maybe we'll just start to see red phones next to the fire-alarm boxes.