Originally Posted by: suzun 
A Heath video on various Green Room solutions would be great.
The answer is, again, what was already written. There's no video necessary.
The exact same procedure you use to set up a vMix Call for production is how you set up a greenroom.
Callers get video from a vMix Output and they get audio from a vMix audio bus.
Set up the video output to give the caller(s) the video you want them to see in the greenroom, and set up the audio bus to give them the audio you want them to hear in the greenroom, just like how you set up the video output to give them the video you want them to see in the production & the audio bus to give them the audio you want them to hear in the production.
If you need a video telling you how to set up and use vMix Call for a production, I'm sure you can find one.
A greenroom is the the exact same thing.
vMix Call is extremely basic in what it can do, in regard to transmitting from vMix to the guest. It takes the video from a designated output and the audio from a designated bus and sends it to the person on the other end of the video call.
That's it. That's all it does with regard to transmitting from the vMix machine to the guest. No matter how hard you try, you will never get it to do anything different.
Whatever you're using it for needs to be done within those parameters.
Whether you're setting up a production or a "greenroom", the steps and procedures are exactly the same, because the extremely basic capabilities of the program are exactly the same.
Originally Posted by: suzun 
Guests are joining the broadcast with their mobile phones using a vMix Call connection,
and the Broadcaster absolutely refuses to use a headset,
This is an entirely unrelated discussion & it's also entirely outside the scope of vMix to teach.
The answer is "Stop refusing to do that".
The second answer is "If they refuse to wear headphones, learn the different types of microphone pickup patterns, proper gain control, proper placement of microphones and speakers, and proper EQ techniques". In other words, become a fully trained audio engineer.
If you need vMix to make a video to help you, the second answer is going to be way too difficult to achieve, and we're back to the first answer of "Use headphones & don't pair speakers with a microphone if you can help it" (which, by sheer coincidence, is also going to be the conclusion you'd reach if you became a fully trained audio engineer).
That second answer is what they do for things like concerts that require microphones and speakers for a live audience.
In cases like this, where headphones or IEMs or earpieces are a valid option, that's what's done.
If you want to do it the other way, you can.
But I can assure you that there's a reason nobody in broadcasting does it the other way unless they have to, and it's because the other way is a significantly larger PITA with a lot more room for error compared to the extremely simple option of "Just wear headphones".
And I can also assure you that Heath is probably never going to make a video teaching you audio engineering.