I guess they really just don't want there to be a definitive set of members or something? Are people still all together at events? I don't know anything about organizing or whatever but that seems like a weird "threat model" if it's just trying to be less visible to the government.
Of course keeping a database or some kind of central computer record is work and requires maintenance and people to be responsible for it, so it's understandable if they want to avoid that. Even a digital process that seems simple at first can become a headache and lots of hours of work. And it's a good thing if they're averse to using something like Google Drive.
If they're really set on doing things in a distributed "peer-to-peer" way, there probably isn't a ton of software that works well like that given the nature of the internet (and there aren't a whole lot of direct in person communication apps). I have no idea about other organizational methods.
I guess the obvious thing is for someone to be in charge of distributing a list of members or messaging everyone. Maybe just more frequent communication in general. Maybe you put people on a rotation in terms of who's responsible for doing a type of task, and others can remind them of their job. That way people don't have to feel like they have to always be tuned in, they can just be prepared for their own turn being the responsible one.
There's literally no advantage or reason I can think of for them to do this other than it seems cool because it's like, underground and word of mouth or some shit. SMS is one of the least secure forms of internet communication, I would rather use Facebook than SMS for security/privacy
Tell them to just throw everybody in a Signal/WhatsApp/Messenger group chat or a Slack channel. Ask them directly to reveal what the purpose of this form of communication is and let them know why it's not a good idea
Internet/data privacy and security within the imperial core doesn't really exist unless you actually know what you're doing with Tails, VPNs, and general real life security practices anyways
