Mumble

Mumble is a program frequently used for voice communication in Lojbanistan. It is free software that runs on Windows, OS X and Linux and provides encryption and good sound quality via speex. To get started, install the Mumble client and connect to a server listed below.

It is a good idea to announce your presence on Mumble to the community, perhaps on IRC or other Forums, either in advance or when you're ready to start chatting.

In fact, some lessons are given by means of Mumble, inquire in #ckule to get in on them.