The interests of synchronous communications in collaborative activities have been recognized by an important number of researches and experiments. Some environments offer the use of synchronous communications as a collaborative learning solution for a group of distributed users. Each user is independent from the other and joins a collaboration activity by his/her own. Such kind of environments is only available for desktop computers. This constraint limits the use of synchronous communications for learning activities. Some activities such as situated learning would benefit from synchronous collaboration technologies. This paper presents a technical solution for mobile synchronous learning activities. First, we introduce educational situations that take advantage of mobility to stimulate participation of the user. Then, we present the technical solution "Platine" developed by the LAAS-CNRS. Platine is a synchronous collaborative learning environment previously developed for desktop or notebook computers. A specific client has been developed for Personal Digital Assistant (PDA).