Originally Posted By: ireckon

With the message to Facebook or similar, there just needs to be a quick burst of data to be sent on a half-ass connection.


EXACTLY! This is the single most important thing to understand - a text message - a short blast of data with multiple retries - will get through when there's not enough signal to establish a voice call. One message to 200 facebook friends might be all you get, and that's sure beats 0 calls that actually make it to the 911 center.

Only a few 911 centers have any SMS (text message) capabilities, and even those are experimental only.