Deregulation is creating competition in the communications industry, allowing telephone service providers, media companies and other firms to offer everything from local telephone services to video-on-demand. Businesses are especially being targeted by alternate providers to switch services. Thus, predicting preference and likely market share for new competitors is a critical business issue. We present a case study of research conducted by US West and Time Warner Communications to quantify the potential for medium and large corporations and government agencies to switch their business from the incumbent local telephone provider to companies offering similar services. Results are based on a survey of 1,3 telecom and datacom managers in twelve cities in the United States, using a phone- mail methodology. We describe our approach to predicting preferences and likely market share using a designed discrete choice experiment. We also show how customer preferences were combined with managerial judgements of the potential behaviors of likely competitors to predict share gains and losses using a dynamic diffusion model.