code: public void grantVoice(Collection<Resourcepart> nicknames) throws XMPPErrorException, NoResponseException, NotConnectedException, InterruptedException {
          changeRole(nicknames, MUCRole.participant);
      }
docs: Grants voice to visitors in the room. In a moderated room, a moderator may want to manage
  who does and does not have "voice" in the room. To have voice means that a room occupant
  is able to send messages to the room occupants.
  
  @param nicknames the nicknames of the visitors to grant voice in the room (e.g. "john").
  @throws XMPPErrorException if an error occurs granting voice to a visitor. In particular, a
  403 error can occur if the occupant that intended to grant voice is not
  a moderator in this room (i.e. Forbidden error); or a
  400 error can occur if the provided nickname is not present in the room.
  @throws NoResponseException if there was no response from the server.
  @throws NotConnectedException
  @throws InterruptedException