Designing concepts for new mobile services and devices, poses several challenges to the design. We consider user participation as a way to address part of the challenges. We show how our effort relates to current and past research. In particular, PD (Participatory Design) has inspired us in developing two participatory techniques. The two techniques are organized around situations either staged or real where users and designers can envision and enact future scenarios: a role-playing game with toys, and SPES (Situated and Participative Enactment of Scenarios). They were developed in an industry-funded project that investigates services for the nomadic Internet user of the future. We then discuss how the techniques help in facing the design challenges. Keywords Mobility, participatory design, games for design, acting out