[noedig]

When I worked at AT&T some years ago they had an entire team of about 50 developers and testers working on identifying problems in AT&T's myriad billing and provisioning systems. This team developed applications that analysts used to reconcile billing with account features, usage, taxes, discounts, etc. This team was very successful in finding both under billings and over billings. One project identified something like $100M in annual under billings. Another project found so many switch/bill mismatches that they just decided to cancel it because they didn't have the manpower to manually correct all the problems or deal with all the customers calling to complain that their bill went up or their feature disappeared.