What do you mean by call home? Do you get some kind of pop up message that says something about internet connection? Is it related to game or Windows? I'd suggest scanning your computer with some kind of antivirus.

It's pretty obvious that FO:NV checks in with a remote server on startup. It starts instantly when my internet is up, and has 25 second delay (presumably timeout when it fails) when internet is down.

None of my other SW does this, so I don't see the Virus association.

You can try to block the game .exe with a firewall. Windows built in firewall should be enough. Game is DRM free, so there should be no problems running it.

Sure, but you still get the timeout delay which is the real annoying part.

PeterScott, hello to you. (^_^)

Unfortunately, this issue is due to Galaxy.dll attempting to contact galaxy-log.gog.com (even if GOG Galaxy has not been installed).

Here is a post that I had created in 2017 (shortly after the arrival of Fallout: New Vegas to GOG.com), outlining the issue, as well as the work-arounds that may be utilized (either of which will work, though, obviously, the hosts file solution is simpler).

Assuming that you are not running Linux, you can still add the following line to your Windows 'hosts' file (located within the directory of C:\Windows\System32\drivers\etc):
127.0.0.1 galaxy-log.gog.com

If you have any questions, feel free to ask.

Run the game direct from its exe--every single game on GOG can be run from its exe, bypassing Galaxy. I use Galaxy only for initial installations and for updating these days. I run all of my games bypassing Galaxy--it's optional.

I do. I have never had Galaxy installed on my system.