More importantly
SMS messages will often get through in poor reception areas and the phone will keep trying until it sends it. There have been lots of cases of people lost at sea / in mountains etc - texting friends to call emergency services.
The local mountain rescue here posts a number to SMS because 911 doesn't support it.
There was one case where somebody in the Caribbean texted the pub in the UK to call 999 to get them to call the local coast guard because he couldn't get a voice signal