A quick way to show actors are in different places (yet communicating with each other) is to write the place name on a sheet of paper (like you do with actor labels) and put them on the ground. Then when someone steps on that, that signifies they are in that location. Think of this as a split screen technique from film making. The split screen ruptures the illusion that the "frame" is a seamless view of reality. We see this technique to simultaneously portray both participants in a telephone conversation.
Here are some examples.
A site dedicated to split screen techniques. I am looking to mine some of the techniques here for future bodystorms.