You raise many good points, and I am glad you see the value of my ‘little science project’ I presented to the CSRIC at the FCC.
As a matter of fact, there is a company that is in existence right now called Smart911.com They have have services in 300+ PSAPs across nearly 30 states, and the Public Safety industry LOVES THEM. They started to provide additional data for residences and cell phones, but I got them to develop an API for ANY PBX to talk to them over the internet, and they in turn communicate to the PSAP with the required encryption.
I just did a webinar on this for IAUG this past week. I am in the process of making it into a YouTube video, as the IAUG webinar is on the member side of www.iaug.org and not publicly available.
Check out http://Smart911Connect.com