A number of studies in psycholinguistics and ergonomics have shown that shared context plays a key role in communication. Many computer-mediated communication tools which convey contextual information have been developed. However, simply making that information available may not be enough to significantly improve communication quality and performance: remote interlocutors must also be given visual cues which lead them to believe that they mutually share this information. The study reported in this article assesses the required efficiency of a series of computer-based functionalities in order to improve remote work communications: a telephone is used as a basic tool. With this functionality, users can designate objects in a shared workspace, in the same way as using deictic gestures in face-to-face situations. They can also view the part of their workspace that is shared with the remote partner before engaging in a telephone conversation. This study was conducted in the field of air traffic control, where controllers need to communicate and coordinate with other remote controllers. Three conditions were compared: these varied in the number of available shared context tools. The results show that with an appropriate context-sharing environment, references to objects are more implicit, and mutual understanding is reinforced. Moreover, both the number of conversational turns and the duration of phone calls tend to decrease. However, the results also highlight some of the limitations of this experiment. In turn, these raise new issues that need to be explored to further improve computer-mediated communications.