Is it possible to implement this function?
It can work as following:
-Ask caller on Busy to press a button to set the CCBS on the called extension
-set a database key for the called extension (CCBS/called/caller :1)
When the called extension hangs up
-on Hangup look for an existing database key
-If an key exists first call the caller and on answer call the called extension
-on answer connect them together
It looks like an easy implementation.