Hi there,
A quick way to do this is to incorporate a boolean variable after the call has been accepted. You then set this variable to be a parameter as an attribute so that call center staff can log into the appadmin page and close the call center. For example:
Start
Accept
If Closed **here closed is a boolean variable set as a parameter**
True
-Goto "True Label"
Fale
-Goto "False Label"
Hope this helps.