Around here on the inland rivers like the Mississippi river, they had about a half dozen mobile channels that I think were in the UHF range. I could be mistaking those with the really old mobile phone channels that were definitely in the UHF band. Either way, the shore radios carried a tone of about 1,000 Hz announcing that the channel was available for use. Tug operators would dial up a number and talk away. The stuff you heard on these inland waterways as well as on the HF channels was about the same content as that heard when the AMPS cell phone band became a thing! Eventually cell phones seemed to have taken over although I can recall hearing the channel available tone for several years after cell phones became the next big thing.
I did not live near any open water like ocean's or the great lakes so I can't say how long those services remained available. I do think some of the HF services are still available on the high seas though but it's been a while since I've tried to monitor any of the old frequencies.
I do remember the "operators" that seemed to handle many of the connections even though a radio operator on a ship could complete the entire call from start to finish.
I also remember inbound calls to a specific person on board a ship would result in being put on hold. I was always told those calls were very expensive!! In most case, the inbound to ship calls were dropped while they found the party being called and then the ship operator would contact a shore operator and have them attempt to contact the original calling party again.
All this was ran by AT&T High Seas Radio back then. I think that explains the high cost of the calls!
I've no idea what a call actually cost but I'm sure it was not cheap. Some also had horrible sound quality due to RF conditions but some were very decent quality also. I think all the calls I heard used USB for the emission type. Man, that was a long time ago now! I remember when a lot of it started being moved to satellite but the old HF method lived on for quite a while.
I would not be surprised if this old HF service is not still supported somewhere out there in the middle of nowhere.