A tax is imposed upon all persons engaged in the business of making sales of service (referred to as “servicemen”) on all tangible personal property transferred as an incident of a sale of service, including computer software, and including photographs, negatives, and positives that are the product of photoprocessing, but not including products of photoprocessing produced for use in motion pictures for public commercial exhibition. Beginning January 1, 2001, prepaid telephone calling arrangements shall be considered tangible personal property subject to the tax imposed under this Act regardless of the form in which those arrangements may be embodied, transmitted, or fixed by any method now known or hereafter developed. Sales of (1) electricity delivered to customers by wire; (2) natural or artificial gas that is delivered to customers through pipes, pipelines, or mains; and (3) water that is delivered to customers through pipes, pipelines, or mains are not subject to tax under this Act. The provisions of this amendatory Act of the 98th General Assembly are declaratory of existing law as to the meaning and scope of this Act.