When we talk about telecom billing then by default it is about retail billing.
As defined earlier telecom retail billing is defined as follows:
Telecom Billing is a process of collecting usage, aggregating it, applying required usage and rental charges and finally generating invoices for the customers.
Telecom billing process also includes receiving and recording payments from the customers.
Retail billing deals directly with the end customer and comes with lot of challenges to meet end customer expectations and regulatory obligations.
A billing is assumed to be successful as long as it is fulfilling following criteria:
Timely Billing: End customer's invoice is being generating on time i.e. nominal date. There may be some circumstances when end customer does not get their invoices on time because of some logistic issues. But it is IT's responsibility to generate all the due bills on due date.
Billing Accuracy: This is most important factor for the customer satisfaction and from regulatory obligation point of view. If billing system is not generating accurate bills then it can lead to serious business issue from legality point of view as well as leaving a customer in unhappy state.