I think academic institutions probably have message boards or forums - I think usenet is certainly a possible model for social interaction, at least in the pre-Empire era, and it's entirely possible that there is a 'dark holonet' not just for actual criminal activity (and we know criminal activity is RAMPANT in the GFFA) - I think there may also be info on bounties available, though I could just be conflating it with Cowboy Bebop in that *g* - but for rebel activity even beyond the Bridgers' type of pirate radio broadcasts. Those broadcasts were meant to be public, as was Ezra's. It's possible that a more private/encrypted network could exist (or several unconnected ones, belonging to cells that later became allies) - at least, it wouldn't bother me if it came up in a story. There had to be some way for the rebellion to get info out to a wider audience, and for random people to join up that didn't involve rescuing princesses from battle stations or being recruited by Fulcrum.