You can initiate a conversation with anyone while you are connected via satellite. But you do need to set up an emergency contact and/or Family Sharing Group if you want to connect via satellite and receive messages that were sent to you while you were offline.

(I’m referring to the "Messages via Satellite" feature that launched two months ago in iOS 18. This is different from the "Emergency SOS via Satellite" feature that has been around since 2022.)