911 calls from unsubscribed devices

[Michael ODonnell]

My understanding is that mobile phone service providers
are required to transmit/relay all 911 calls regardless of
whether the originating device is registered/subscribed to the
provider in question.  If so, what kind of (preferably minimal
and unobtrusive) HW/SW would a generic laptop (running Linux,
of course) have to be equipped with to exploit that requirement
to have a basic 911 Panic Button capability?

I assume that, ideally, a 911 operator would like to
have a conversation with the caller to better assess the
nature/urgency of the emergency, but I also assume that's not
strictly necessary as long as location info is included in the
transmission, as obtained either via GPS or tower-triangulation.