Have they open sourced the server? Revival projects should always do this, otherwise they are preserving nothing. A single point of failure means someone else will have to reverse-engineer the protocol and write the server software again in the future. Do it for posterity!
Why wouldn't a project like this be OSS? How do they expect to monetize? People buying dialtone subscriptions as a social network?
There's another project, P3OL, that's also closed-source. I assume they're connected somehow.
P3OL makes 100€/month through Patreon, I guess that is also this project's reason to stay closed-source
I'm unable to find the server, but it looks like they've released some protocol analysis tooling: https://github.com/iconidentify/wiretap