Thanks, although I left 'video' only in the camera setting, mic input was working fine via web browser and my wife heard the sound coming from the camera. So it seems that 'video and audio' option is for streaming only, not two-way - with audio included, you only get the sound from the video.
However, just for sake of it, I enabled audio and video on both sub and main stream, it didn't make a difference at all and there is still no -'mic' icon on IVMS so it must be on software side of thing.
Because of this and like you have said about WP version, I decided to try it out on Android tablet (Nexus 7 with Lollipop version 5-5.1) - The Play store said that iVMS-4500 is incompatible, yet Lollipop has the one of the highest share in Android OS, if not the highest.
I guess that if I don't find any app that supports audio two-way then this camera will have to be returned. It is getting a bit ridiculous at this point, I mean I could have set up my old & disused netbook and install Skype on it and ticked box that says 'auto receive call' and then I would be able to use my voice while I am away? The only one issue is that inbuilt webcam does not have IR support!
Is there an IP camera that really 'does what it says on the tin' with audio two-way support out there in the market?