I have a Current Project a Paging Application.
4 Inbound calls at once and 4 outbound calls at once can be done. But the catch is to que the dialed outbound code so even though there are 4 outbound trunks always available only 1 number/ Code Back to the MITEL can be dialed at once QUEING the page so to speak ..
So the paging system can play the pages in order they get from the asterisk and a user doesnt get a busy tone if the page system is busy so a max of 4 recordings at once but it can have about 6 waiting to be played not that the number will ever get that high...
Outbound number queing....
Attached a JPG of a quick diagram.
not sure if .CALL files can be done for this.