jeffphil wrote:What's the best solution to fall back to the normal POTS line and ensure that if the technology goes haywire the line can be freed up for a 911 call even if it were up until that point 'off hook' on the Asterisk box?
There are ATA's that have both and FXO and a FXS port on them - you can then configure them so that certain numbers (like 911) just get bridged between the two and not handled by the Asterisk server. Here is what the setup would look like: Your incoming PSTN line would be connected to the FXO port on the ATA, the analog phone is plugged into the FXS port of the ATA and the ATA is plugged into the network. You can use the FXO instead of the X100p card, or just have it there in case of a 911 call (i think the X100p works better as an FXO). I'm not sure how configurable these ATAs are the concept of the Bridged call has alot of possibilities. I also don't know what happens in a power faliure but a cheap UPS should power the thing for many hours.
I have been playing with one of these ATAs (Grandstream handytone 488) but have not done enough testing to answer all your concerns - but maybe something to look into