Maybe you misunderstood but the SOS function in the iPhone is satellite and not cell based and lets you send texts to emergency services.
Discussion
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.