Invite online visitors to record voice comments, language exercises, testimonials or any audio content within the regular WordPress comment area.
See http://www.evoca.com for more information on signing up.
Evoca also offers the Evoca Audio Recorder, which users typically place (embed) in the sidebar of a blog or website. It does not require visitors to have an account to use the recorder. See http://wordpress.org/extend/plugins/evoca-audio-recorder/