As Mike said, text messages and some 911 signals require much less
power and signal to go through. (Mobile phone software enforces a
"quality of service" threshold; if it cannot be met or exceeded for a
voice call, it will not go through, but this threshold is very
different for text and emergency calls.)

I landed out ~50 miles south lf Moriarty a couple of years ago and my
mobile didn't work; it showed a weak analog signal but wouldn't place
calls. But 911 worked, and when I explained by situation to the
operator, she got called my crew number and we got hooked up.

~ted/2NO