I think this can work. Put a battery backup in the ATA, to power the
GPS and real time clock. The ATA will maintain the internet-routable
address it's using (not necessarily it's own IP address) indefinitely.
If the ATA determines it's routable address (or /23 or whatever subnet)
has changed since being disconnected, it prompts (via voice menu on
connected phones) that it needs to be taken outside and re-GPS'ed.
Flashing light on the box confirms when GPS has synced it's location.
Take it back inside, plug it in, and all is ok again. Or something
along those lines....
So will you block all useage until you do so?
Any voluntary compliance solution will fail the CALEA aspect.
And I recall reading somewhere in the trade press that the reason
some cellular carriers went to GPS-based solutions was they could
not meet the FBI specs for accuracy with tower-timing solutions.
And needless to say, I can think of many places both cellular and
VOIP cam be used where GPS will be worthless.
One other point: both the FBI and EMS want to know which office
on which floor of the Empire State Building you are in when you
call, not just a 2-D circle of X radius.