At this very moment, I'm out in the woods typing away on my laptop. I have an internet connection, and my phone can use that connection to send text messages, but I have no voice phone service.
How can I contact emergency services from here?
I'm in the United States (San Jose, specifically¹), so normally I'd call 911. Currently the local 911 service doesn't support text messaging.
¹ More specifically, I'm in a cabin in the mountains just outside San Jose, 20 minutes drive from the nearest hospital. There are a surprising number of places in these mountains where you can find a wi-fi signal being broadcast from some hidden cabin, but very few places where you can get a cell phone signal.