Non-billable calls

I’M DOING BILLING ANALYSIS FOR A LONG DISTANCE CARRIER FOR AROUND 2 YEARS AND NORMALLY ALL THE CARRIERS ARE CHARGING WHEN YOU HAVE AN ANSWER SUPERVISION OVER YOUR SWITCH, DOOESN’T MATTER IF THE SOUND IS BAD OR NONEBODY IS TALKING, MANY COUNTRIES HAVE OLD SYSTEMS WITHOUT ANSWER SUPERVISION TO TAKE CARE OF THIS PROBLEM MANY CARRIER ARE GIVEN LIKE A GRACE OF PERIOD FOR THE CALLS, IT DEPENDS OF THE COUNTRY AND HOW FAST YOUR LINES ARE CONNETING, MANY TIMES WHEN YOU DIALED AN INCOMPLETED NUMBER YOU COULD GET AN ANSWER FROM YOUR DESTINATION LOCAL COMPANY, IT MEANS YOU HAVE ANSWER SUPERVITION AGAIN, SO IN REALITY YOU HAVE TO TAKE A PERSONAL OPINION SOME TIMES (POLICIES) FOR WHICH CALL YOUR ARE GOING TO CHARGE.