A mobile unit as well as a method for time-stamping a first message of the first mobile unit to a second mobile unit are provided. The method includes the steps of: determining a roundtrip time between the first mobile unit and a base station, receiving the first message sent by the first mobile unit in the base station, adding a timestamp to the first message in the base station while taking into account the roundtrip time, and sending the time-stamped first message to the second mobile unit.