Up until the early 1980s, most telephone networks in the United States were operated and owned by AT&T. Since AT&T was a monopoly, the firm dictated the services and equipment available for customer use and their charges. Although this arrangement might not have been suitable for their clients, it was simple and straightforward. With time, new entrants into the industry were established, and billing overcharges became rampant. Here are a few tips to keep in mind when managing corporate telecom expenses using Excel.