From Benjamin Mayo, 9to5Mac, yesterday:

In an investor note, Ming-Chi Kuo today said that he expects the upcoming iPhone 13 models to feature a low-earth-orbit (LEO) satellite communication mode. This would allow an iPhone 13 user to send messages and make phone calls, even when they are not within standard 4G/5G cell tower coverage.

And today, from Juli Clover, reporting on this paywalled Bloomberg article:

There are at least two emergency features that will rely on satellite networks, and while satellite technology has been in the works for years, these capabilities are not likely to launch in 2021.

The first feature, Emergency Message via Satellite, is designed to let users text emergency services and contacts using a satellite network when there is no signal available, and it will be integrated into the Messages app as a third communications protocol alongside SMS and iMessage. It will feature gray message bubbles rather than green or blue, and message length will be restricted.

And:

The second feature will let users report major emergencies like plane crashes and fires using satellite networks. It will be similar to a “911” call in the U.S. and can provide information like a user’s location and medical ID, in addition to alerting emergency contacts.

Sounds like this will be built into the iPhone 13 hardware, not intended as an alternative to traditional carriers, and those grey bubbles won’t roll out until next year.