A central accounting and billing system for enterprises providing service and supply operations for business machines located in a plurality of customer locations employing a fleet of vehicles each carrying a trunk inventory of frequently required repair parts and supplies. An ERP system at a central location generates machine-readable identification tags which are applied to parts and services carried in each of the trunk inventories and are applied to the machines to be serviced. Smart handheld devices such as cell phones contain programs which allow the identification tags to be read and communications to be established to the central ERP system relating to transfer of goods and supplies into and out of the trunk inventory and to the businesses and also the time involved in servicing particular machines at particular businesses in order to generate bills from the central enterprise to such businesses.