Hi Alan,
Not sure what you mean so...
Moodle is written in PHP which isn't suitable for directly implementing voice over internet protocol (VoIP) or web conferencing. For that you need either a Java media server, e.g. Red5, or Flash Media Server (as used by Youtube), or all users/participants need to have a VoIP client installed on their computers, e.g. Jabber, Skype, or GoogleTalk.
If you only want to record and playback audio, then there are some Java and Flash client based plugins for Moodle that do it well, e.g.:
https://moodle.org/plugins/view.php?plugin=repository_recordaudio (Flash client)
https://moodle.org/plugins/view.php?plugin=assignment_onlineaudio (Flash client)
https://moodle.org/plugins/view.php?plugin=assignsubmission_onlineaudio (Flash client)
http://gong.ust.hk/nanogong/ (Java client)
If you want real time online conferencing, classrooms, face to face, etc., this is beyond the capabilities of Moodle and requires some 3rd party software or services that integrate with Moodle, e.g.:
https://moodle.org/plugins/view.php?plugin=mod_bigbluebuttonbn
https://moodle.org/plugins/view.php?plugin=mod_wiziq
https://moodle.org/plugins/view.php?plugin=mod_openmeetings
https://moodle.org/plugins/view.php?plugin=mod_netucate
https://moodle.org/plugins/view.php?plugin=mod_videoconference
https://moodle.org/plugins/view.php?plugin=mod_vitero
I hope this helps!