One of the greatest challenges in the design of speech recognition based interfaces is about the navigation through the different service hierarchies and structures. On the one hand, the interactions based on human machine dialogues force a high level of hierarchical structuring of services, and on the other hand, it is necessary to wait for the last phases of the user interface development to obtain a global vision of the dialogue problems by means of user trials. To tackle these problems, Telefónica Móviles España has carried out several projects with the final aim to define a corporate methodology based on rapid prototyping of the user interfaces, so that designers could integrate the process of design of voice interfaces with emulations of the navigation through the flow charts. This was also the starting point for a specific software product (MEDUSA) which addresses the needs of rapid prototyping of these user interfaces from the earliest stages of the design and analysis phases.