Creating the Feature Request on behalf of SP Global, Inc.
Currently, you can view if a Registered User or Endpoint is "online" by viewing the "Contacts" section of the Cloud Applications by a presence of a "Green Dot" next to their name.
However, you are not able to view if this User is currently in a call. To prevent mistakes of individuals from disturbing an End User who is currently in a call, it would be a great feature to include a visual indicator with the contact name that visually alerts a user to the fact that they are already involved in a teleconference. Ideas that might work could be that the contact might display a concentric ring (an outer green ring and an inner green ring separated by a white border). Another possibility might be a checkmark superimposed on the green dot icon.