I hang around in the middle of nowhere in dangerous and stupid places a lot for days. It'd be nice to bounce the odd message to family to inform them that I'm not dead.
There's no denying that smartphone messaging via satellite is game-changing in this space (and I hope my Garmin Fenix watch will one day have 2-way SOS messaging capability integrated into it) but I wouldn't trust a smartphone for this.
I would like 2 completely different channels to communicate over.