Perhaps I can help. My partner and I use the ZipDX conference bridge to allow people to participate
a weekly podcast/hangout. We've done this since 2008. Prior to Hangouts, the show was hosted on
Talkshoe. The show is about telecom topics, so we have a strong background in telephony.
A ZipDX conference is accessible via access lines in 60 countries. Also, the service can dial-out to anyone, anywhere.
Further, the service has a WebRTC-based WebPhone that allows HDVoice connectivity from computers running Chrome or Firefox.
Finally, the service is available via SIP. That means that it can be interfaced to vMix using a standard SIP soft phone. I happen to use Bria.
All audio processing happens using 16 KHz sampling, delivering an 8 KHz audio channel. The service supports G.722 and Opus. It's not production grade, but vastly superior to a traditional telephone call.
Here's why ZipDX is especially useful in this regard. A ZipDX conference has multiple "breakout rooms." These are essentially private side-rooms, separate from the main conference floor. You can use this mechanism to queue calls into your production.
You can use one of these rooms as the the "broadcast booth" so that anyone in the room can be heard in your production.
Then use the main conference floor as a "Green Room." A place to hangout until the guest is needed in the live production.
One of the rooms has what we call "one-way glass. Anyone in the room can hear the conversation on the floor, but cannot be heard on the floor. If participants in the room have a local conversation the discussion on the floor is automatically ducked. When the local conversation is quite thy return to hearing the discussion on the floor.
You use our web-based dashboard to move people between rooms. It also allows you to mute/unmute people. Most importantly, it allows you to see who is connected.
ZipDX is not free. It's priced per-minute, per-connection. SIP and webphone connections are the lowest rates, since we don't have to pay intermediate networks for the transit.
Disclosure - I work for ZipDX and they sponsor said podcast. Their sponsorship extends solely to the use of the service. They're not pursuing this sport of business, but I'm happy to demo it to anyone who has a real project.
