In this paper, we describe a new methodology to develop mixed-initiative spoken dialog systems, which is based on the extensive use of simulations to accelerate the development process. With the help of simulations, a system providing information about a database of nearly 1000 restaurants in the Boston area has been developed. The simulator can produce thousands of unique dialogs which benefit not only dialog development but also provide data to train the speech recognizer and understanding components, in preparation for real user interactions. Also described is a strategy for creating cooperative responses to user queries, incorporating an intelligent language generation capability that produces content-dependent verbal descriptions of listed items.