Mine when locked has a small touch section labeled 'emergency call'. I assume it goes through to 911 (or relevant number). I'm tempted to press it but it's not an emergency.
I assumed most phones had something similar.
I went to it. I leads to a special dialer. Instead of voicemail the button leads to a special emergency contact (or list). It only shows 4 inputs on top so I am guessing that is the limit so you can't dial anything but emergency services (that are 4 numbers or shorter). Then it goes back to my lock screen.