In this paper, we present a new shape-based display technique for mobile phones: A rotatory deformation of the phone’s chassis, resulting in a tapering between the phone’s front and back panel. It draws on proprioceptive skills of the human hand, which we hypothesize to be sensitive to paralellism and tapering of two opposing panels. We present a number of applications for such an actuation system: Interactive Feedback, User Notification, and Ambient Display. The proposed system is evaluated in a user study, which results point to certain advantages, as well as drawbacks, in comparison to other mobile actuation systems. We conclude by discussing areas in which tapering-based deformational displays may be used advantageously, and how the proposed system may be improved in the future. Author Keywords Shape change, mobile phone, tapering, feedback, notification, ambient display, hand, tactile, haptic. ACM Classification Keywords H5.m. Information interfaces and presentation: Miscella...