You could also just have the recipient in the first part of the message block so that the devices that aren't the recipient either just ignore the message or can't decode it.

My biggest question is how do you send a signal to a satellite with your mobile phone. And they're even saying without additional hardware which makes it even more difficult.

Or are they just hoping that there would be no obstructions from your device and the satellite, no roof and a good sunny weather?

Although my knowledge is lacking, my understanding is that 2G has good range at the expense of low data rate. But I have a feeling that many modern phones no longer support 2G, since (at least here in Slovenia, Europe) many providers have over the years lowered or totally removed the number of 2G towers.

It's supposedly already been demonstrated by a different company: https://techcrunch.com/2021/09/29/lynk-demos-global-satellit...