I met a person who runs a competitor with similar restrictions. Their suggested architecture was basically to use this for notifications for very remote sensor

I met a person who runs a competitor with similar restrictions. Their suggested architecture was basically to use this for notifications for very remote sensors: "battery below 20%. Come help" etc The other way is for things like Garmin InReach: "Send message 1" (which is "I'm ok and don't need help") etc.