In this work we investigate the effects of rephrasing the user's input on two mobile spoken dialogue systems. We argue that for specific kinds of applications it's important to confirm the understanding of the system before obtaining the output. In this way the user can avoid misconceptions and problems occurring in the dialogue flow and he can enhance his confidence in the system. Nevertheless this has an impact on the interaction, as the mental workload increases, and the user's behavior may adapt to the system's coverage. We will focus on two applications that implement the notion of rephrasing user's input in a different way. Our study took place among 14 subjects that used both systems on a Nokia N810 Internet Tablet.