1.There is only IE supports 2 way audio. Other web browsers support 1 way audio in VLC mode. After you login the camera by IE, you can get the 2 way audio by clicking this button. 

2. For VLC mode, there will be audio in default. If your web browser always says no plugin found, please upgrade the new firmware. 
http://www.rewont.com/web/firmwaredownload.html
3.If you could not get any audio in IE, please change the Internet Security Options:
http://www.tenvis.com/support_service-69.html 
4. There is no audio in our mobile phone application. However, you could find some 3rd part software which will support our cameras with audio.