As computing moves in the direction of pocket-sized portable devices, speech and pen will become input modalities of choice. However, little currently is known about how people are likely to speak and write to future interactive systems. This paper describes a. new simulation technique designed to support a wide spectrum of empirical studies on the characteristics of spoken, handwritten, and combined pen/voice input to future interactive systems. The simulation technique aims: (1) to provide a tool for investigating interactive handwriting and pen systems, on which no simulation research currently is available, (2) to devise a technique appropriate for comparing people's use of speech and writing, such that differences between these communication modalities and their related technologies can be better understood, and (3) to support a very rapid exchange with simulated speech, pen, and pen/voice systems, such that interactions can be subject-paced. This paper outlines the specifications, general environment, and capabilities of a new semi-automatic simulation technique developed to achieve these goals.