Facebook has just announced that it now allows group voice calls to everyone through Facebook Messenger. As you can see, the new feature will be available to all social network users during the next 24 hours. 
So if you don't have it yet, make sure you have the latest one information of the application.
For those who already have this feature on Messenger, tap the phone icon to start a group call. The next screen will allow you to select the people you want and invite them to your conversation.
Of course you won't be able to chat with many at first as everyone will have to install the latest version of the application.
Also for the moment the application does not support video conversations, but it is probably a matter of time before Facebook activates them with a next update.
Facebook has not yet reported how many can take part in group voice calls.
