for the subscribed service. The invoice is then sent to the customer. The bill amount is then col- lected from the customer using the deferent payment options supported by the service provider and the customer account is updated. 2. Rating and discounting: This is a service level process. A predetermined rate is applied on the service consumed to come up with the amount due for a specific service usage. On the computed amount, discounts or other rebates are applied to come up with the billable amount for which an invoice can be generated. 3. Billing data collection: This is a network level process. Service usage is calcu- lated using records generated at the network elements on which the services are offered. For simple voice service, call detail records (CDRs) make up the billing data (records) that is collected. Information in the billing data gen- erated by the network elements are processed to get usage information on which rates can be applied. Billing is no longer limited to a method of collecting money from the customer for services used. It has evolved into a process that has its own independent standards OSS/BSS Functions and can be a key differentiator for a service provider. Billing is often used as a strategic tool to get and retain business. The results of the renewed approach to bill- ing has led to different types and models. Some of the key terminologies used in billing that the reader has to be familiar with are: 1. Account: Each customer is handled as an account in the billing system. While multiple services can be associated to an account, usually one account will have only one customer. For competitive pricing, some service providers are offering family level accounts, where different users are linked to a consoli- dated account for generating a single bill. 2. Service: Any tangible or nontangible offering from a service provider for which the customer is billed makes up the service. The package that is offered as a service varies based on the service provider. 3. Plan: This is a bundle of ser