If the latest speculation from analyst Ming-Chi Kuo is true, it means you could make calls from the mountain or do video chats while at sea.
Source: Analyst: iPhone 13 may be a satellite phone | Computerworld
Current service plans range up to $200/month for sat phone service, and offer voice capabilities. And currently, GlobalStar does not really service ocean coverage.
Perhaps a limited text message service, via iPhone 13, similar to how Garmin InReach communicators work over the Iridium network. But “video chats while at sea” from a handheld iPhone 13? Doubt it.