NavList:

Bob Goethe, you wrote:
"One can choose the time server used by his cellphone."

That may be something local to your service. There's no option on my phone to select a time server for the phone itself (though some specialty apps, of course, provide such options). Instead my phone, and all other US phones that I have examined, get their time from the service provider's network (from the "cell towers") or by manual entry. Anyone else? Other countries?? Can you manually enter a time server in your phone's settings?

You added:
"I use a time server that gives UT1 times."

Which one? I didn't know there were actual time server's broadcasting UT1 (makes sense, just news to me!). Since the difference, DUT, between UT1 and UTC is just a fraction of a second, there's another issue here. How often does your phone check in to get an update from the server, and how much does the phone's internal clock drift between updates? In short, how close is to UT1 after, let's say, six hours? Or twelve hours?

You concluded:
"As far as I'm concerned, they could just continue indefinitely publishing the Nautical Almanac with UT1 times."

Yes, I agree. That's the simple solution and the best solution. And bear in mind that "the" Nautical Almanac is a rapidly disappearing concept. People still but "official" Nautical Almanacs for reasons both rational and ir-. But we can now safely get our navigation data from numerous other sources which are almost all derived from the same sources (JPL etc) as the official almanacs. It may well happen that most "app" almanacs will allow an option to use either UTC or UT1. Let's just hope they make it blatantly obvious which one is in use!

Frank Reed