At the very centre of the white cube, a dot of light, floating.
The intersection of two laser-beams.
A continuous sound made of thousand of voices coming from real time or pre-recorded phone conversations. Something close to white noise but different enough to make the audience feel the origin of the sound.
When visitors cut one of the beams, the sound stops.
Everything happens as if the contact of the two beams would make the whole communication process possible.