We present the first user study of out-of-turn interaction in menu-based, interactive voice-response systems. Out-ofturn interaction is a technique which empowers the user (unable to respond to the current prompt) to take the conversational initiative by supplying information that is currently unsolicited, but expected later in the dialog. The technique permits the user to circumvent any flows of navigation hardwired into the design and navigate the menus in a manner which reflects their model of the task. We conducted a laboratory experiment to measure the effect of the use of outof- turn interaction on user performance and preference in a menu-based, voice interface to voicemail. Specifically, we compared two interfaces with the exact same hierarchical menu design: one with the capability of accepting out-ofturn utterances and one without this feature. The results indicate that out-of-turn interaction significantly reduces task completion time, improves usability, and is preferred to the baseline. This research studies an unexplored dimension of the design space for automated telephone services, namely the nature of user-addressable input (utterance) supplied (in-turn vs. out-of-turn), in contrast to more traditional dimensions such as input modality (touch-tone vs. text vs. voice) and style of interaction (menu-based vs. natural language).