This is interesting. Doing a little research, it seems like for the extra cost (with Verizon), it's seamless. Apple gives you the Skylo/Spacemobile service for free. It works but you have to go through a process every single time to text AND receive.
Looks like with the Starlink upgrade for $10 a month (free with T-Mobile) it works like regular texting, sending to the satellites in the background.
I've used sat text via verizon and an iphone (which is apparently globalstar sat) a lot this summer. It works fine, but is clunky. I don't need it to be more seamless for what I've used it for, I wouldn't pay extra for better at this point (noting that a PLB is used for immediate communication). We did have a few reliability issues, but overall it works 95% of the time.