I just found about this feature on new iPhones version 14 or later and mine is a 15.
You can use satellites for texting if you update to iOS 18 which was released last week. It's an update you have to look for. Here's how....
Go to updates and look below the current update and it might say "other updates available" and click on 18. You might have to look for it like I did.
Here's a bulletin from Apple on how to use it.
With iPhone 14 or later (all models), you can connect your iPhone to a satellite to text emergency services, request roadside assistance, message friends and family, and share your location — all while you're off the grid with no cellular and Wi-Fi coverage.
support.apple.com