Obviously implementation will get better as tech marches forward, but I have played with the Sat connectivity in the new iPhones (They have sat SOS baked in). So far, it has not made me want to give up my Garmin InReach.
The phone needs to be held pretty steady, and is kinda touchy about horizons, and being blocked. My InReach, I can pull out my phone, fire off a text, put the phone away and keep hiking and the Garmin will get my message out as I go. Sat texting bandwidth is lower then cell SMS too, so the messages take a little longer to send. I haven;t sent an iPhone SOS, but I can get it to go in and out of connectivity just by moving it, so I can imagine having to hold it pretty steady for 2-3 minutes to get the message out. Not a big deal if you need an SOS, but annoying if you are firing a simple text.
I have no idea if it's an antenna issue (the phones obviously receive sat signals just fine on their GPS antenna),or a software issue, or a satellite constellation issue, or what.
Also the dedicated sat communicators can get you weather and maps (sometimes) which is nice. I'm sure the phones will get there, but my understanding is that starting off it's just SMS functionality.
What I really wish is that elon would make me a Starlink terminal about 9" on a side, and let me turn the service off and on like Garmin does. Then I could mount it on the overland rig next to the HAM antenna.
So for now, I'm still glad I have the Garmin.