With the development of personal wireless mobile devices, direct data exchanges between several devices, known as spontaneous communications, will become increasingly important. In such a context, the communication time is limited according to devices' mobility. Despite the limited communication time, applications often require atomic commitment between two mobile devices. In this paper, we present a protocol to address the problem of atomic token passing from one mobile device to another, in the context of spontaneous communications. The protocol relies on a variant of the two-phase commit protocol. Our approach is based on dynamically adapting the communication time in the two phases of the protocol.