Some tasks supported by educative and collaborative tools can be more realistic and accessible if they are tackled using mobile devices. This approach allows students to benefit from the mobility features of this kind of devices, which are expected to revolutionize teaching in the next decade. In this paper we present an application called DomoSim-Mob to carry out practical activities of domotical design using PDAs. We introduce the task of collaborative planning of design which is supported by DomoSim-Mob and describe its materialization starting from the user tasks supported by the previous desktop computer version.