There are many instances where a telephone call charge needs to be avaialable immediately after a call is made. Usually, for a fee a telecommunication provider can provide call charge for a particular call. Call charging systems provide this information automatically without recourse to a telecommunications service provider. The application of call charging systems include private automatic branch exchange line cards, home telephone bill monitoring, monitoring telephones in a telephone cafe booth or payphones. This paper examines the design of hardware and software of the sub-systems for a subscriber based call charging system.