If you set answer supervision to yes and none is returned the audio will not cut through so both parties can hear each other/or the dialed digits may not be sent out at all . It has been years since I worked on one but I seem to recall a cos option to log smdr on short calls . But I maybe thinking of another old system so don't hold that as gospel . Plus there are various other intermitten issue it will cause depending on the type of trunks installed .

Let It Be , I live in a Yellow Submarine . SCCE