So far we've only learned that 2-way comm will come to all older phones (14 and later) that support satellite. Very basic SMS, no photos, very low bandwidth. You can send to any number, but receiving is more complex (details in this doc below). Sounds like the other party has to be in your favorites or emergency contacts, they have to tap an extra "send by satellite" button, and you have to continue tracking by moving the phone as directed. All makes sense
With iPhone 14 or later, you can send iMessages or SMS messages via satellite when you’re off the grid with no cellular and Wi-Fi coverage.
support.apple.com
2-way messages USA / Canada only for now, 2-way SOS from anywhere as before (except Armenia, Belarus, China mainland, Hong Kong, Macao, Kyrgyzstan, Kazakhstan, and Russia in the small print)
Still no details on what happens after "free for two years" is over