This dissertation is concerned with the implementation of a Billing System in a Telecommunications Company in Ireland, in particular Esat Digifone. Esat Digifone launched in 1997 and has grown from strength to strength in a short time period. Esat Digifone launched their Prepay service in the Irish market place on 25th November 1998. Mobile Communications has really become a powerful and very competitive industry in Ireland and throughout the world. Due to this competitiveness it is important for a Company to install capable and powerful systems, one of the most important being the Billing (Customer Care) system. It is the purpose of this study to access all aspects of a Telecommunications Company, namely Esat Digifone, when dealing with a Billing System within such an industry. It is the belief of the author that Esat Digifone has been successful to date and this has allowed Digifone to be more competitive than before. In order for Digifone to continue to enjoy such growth and become the market leader they must continue product innovation and therefore ensure that the Billing system they use is more than capable to handle such products. This dissertation evaluates the concept of Billing Systems and the amount of work involved when implementing a change to such a system.