Unfortunately there's always going to be meta-gaming, and even if there's nothing available for players to use outside of the game to help them, they will create it. Voice coms like Mumble, Ventrillo, and Teamspeak are great examples of this and they have existed for ages before the times of our Discord Overlords.
Rather than trying to prevent such a thing, I think SbS is making plans around the systems that players already use. There is no in-game VOIP, players would have to use another program like Discord to talk to each other if they want to, and it's not a planned feature for in-game communication either. However there's several reasons players should think carefully on the reasons why they should or shouldn't use VOIP for something plus it's immersion breaking for the player, if the player chooses to use it.
As Caspian stated in the older Chat System DJ: The other caveat is that unlike in most games, organizations/guilds do not automatically get a private chat channel. If you want to get the player aliases of your guild members and invite them to a private channel you may do so, however it's not automatic. This is done for two reasons. First, it breaks the immersion. If you want to have a guild meeting, then rent/purchase a guild hall, gather, and hash stuff out face-to-face. Being able to manage guild business remotely means guilds can spread out so far as to not be able to travel back to their origin city for meetings. This violates some of the realism of the world I'm striving for. Can players just use a VoIP technology to have guild meetings anyways? Sure. But this gets my point across.
As well as another comment on use of outside programs by Caspian:
... while we're not necessarily providing integrated VoIP, it's common in the more serious MMORPG organizations to require VoIP for organized events. No matter what features we add to allow for (or encourage) espionage, jumping on Discord, Vent, TS, etc.. is a good way to counter such attempts. Does this encourage more social interaction? Yes. Was that by design? Yes. It's shown that on the internet, deviance/toxicity is inversely proportional to how much anonymity one perceives they have. By encouraging players to use VoIP it should improve the overall player experience. We shall see.