Sending the audio message from the iOS and android devices on Facebook messenger. It is very convenient to send the message from the mobile devices which might come handy in some situations.
To send voice message, tap the + button beside where you traditionally type a message in the Messenger app. Then select Record, holding the button down to speak. When you release the Record button your voice message will be sent to your recipient.
You must not confuse the free call with free data usage -- you'll still have to pay for the data usage.