I apologize in advance for improper use of terminology. I don’t really do telecommunications for a living, but do have a FreePBX/Asterisk PBX running in a small business.
I ran into a possible scenario for which I wasn’t sure of its resolution. Hoping someone more expert can clarify things.
Here’s the scenario:
Start a simple internal conference using freepbx with no PIN nor a leader. Say extensions A & B are in the conference. Extension C calls an external conference number (like an 800 number), once connected, blind transfers that call into the internal conference, then calls the internal conference. For the sake of this example, say that callers D, E, & F all called in individually to the external conference number as well. Let’s also assume that the external conference is also simple and will remain active as long as one caller is still connected.
So we have internal callers A, B, and C connected to an internal conference along with an outside line (the external conference) also connected to that conference.
So when the meeting is over and everyone hangs up, what happens? Will the internal conference consider the external conference an open line (and vice versa) and not hang up? I have a feeling that it won’t… that the two conferences will remain connected, each believing that there is an active caller and simply never hang up.
This is, of course, assuming neither conference is particularly smart, like listening for dead silence to assume that the conference is over or hanging up when the leader does.
So is my conclusion correct? That short of some specific key sequence to tell the external conference to hang up or a leader dependent conference, that simply placing the internal extensions on their switchhooks won’t hang up the trunk line, ie the connection to the external conference?
Did my question make any sense? 
Thanks in advance.