A hellbanned player can type and voice chat as much as they want, but nobody will ever see or hear it in game. Admins will see it in the server logs.
Admins can hellban players by adding IDs to the server's Mod.ini with the following format:
[Hellban.Server]
PlayerIDs=xd83abe496ca401497b5adf4e412bf2c
PlayerIDs=yd83abe496ca401497b5adf4e412bf2c
PlayerIDs=zd83abe496ca401497b5adf4e412bf2c
Local clients mute players locally in their own Mod.ini:
[Hellban.Client]
PlayerIDs=xd83abe496ca401497b5adf4e412bf2c
PlayerIDs=yd83abe496ca401497b5adf4e412bf2c
PlayerIDs=zd83abe496ca401497b5adf4e412bf2c
A menu will be built soon to allow for mid-game hellbans by rcon admins, and allow players to mute people as they wish if playing a game mode with a non-standard HUD (Which as of now is everything but Blitz probably)
In the meantime, IDs of annoying players can be found at UT4Stats.com (the last part of the player_history URL is the ID you want. Remove the trailing /)