Mumble

In addition to voice it is also possible to do text chat via mumble. The security of this is pretty good provided that you do it via Plumble and Orbot on mobile, but compared to other options such as XMPP/Conversations or Tox the security is not as good, since the mumble server currently doesn't support forward secrecy.

Within the software center search for "mumble" and install the client then run it. Skip through the audio setup wizard.

Click on "add new" to add a new server and enter the default domain name for the Freedombone, your username (which can be anything) and the VoIP server password which can be found in the Passwords section of the Administrator control panel. Accept the self-signed SSL certificate if you don't have a Let's Encrypt certificate set up for your default domain. You are now ready to chat.

Install F-Droid

If you don't have Orbot installed then enable The Guardian Project repository from the drop down menu and install it.

Search for and install Plumble.

Press the plus button to add a Mumble server.

Enter a label (which can be any name you choose for the server), the default domain name of the Freedombone or preferably the mumble onion address as shown on the About screen of the Administrator control panel, your username (which can also be anything) and the VoIP server password which can be found in the README file on the Freedombone.

Open the settings. Select General, then Connect via Tor. This will provide better protection, making it more difficult for adversaries to know who is talking to who.

Selecting the server by pressing on it then connects you to the server so that you can chat with other connected users.