Me and a few of my partymates had the message cantrip, and I pointed out that due to the cantrip's effects, we can virtually "have a telepathic group chat" via those of us who have the cantrip.
At first, I tried to stick to the illusion that I act as an intermediary to those in my range but doesn't have the cantrip, and that I identify myself before I speak up ("Megane here... blah blah blah").
The more it went on, the more the facade broke and eventually we were just discussing strategy under the assumption that it's "message-mediated".
The DM allowed it, and later gave all party members an artifact that has the following effects:
- anyone with the artifact can telepathically send a message to everyone else who has the artifact (within range)
- those who have the artifact can hear any and all such messages sent through the artifact (within range)
Later on, even the range stipulation was handwaved off (within limits—basically those who are in the same scene are assumed to be in range of each other).
Near the end of the campaign, the DM reminded us through an NPC that we're all "staring off into the distance" whenever we use this telepathic "group chat". We basically forgot to talk to each other normally (in character).