You hope you do. It's OK, for now, but gosh, I wouldn't want to have to rely on a cell phone that's droppable...
But it sure is better than not having that.
Discussion
For sure if I was mountaineering or back country hiking I'd spend the money for something more durable and with better battery life.
I solo hike and I'm often in areas with no cell coverage and having a means to send an SOS is a comfort.
Maybe you misunderstood but the SOS function in the iPhone is satellite and not cell based and lets you send texts to emergency services.
I'm very well aware. I have several friends who have new iphones with that function, but, it's very limited, and takes a long time at times to connect to a satellite to send an SOS, and is very sensitive to phone directionality. It's usable, but not intuitive in a panic situation.