[pvonk]

It seems to me that if you need to wait for a return call, then there's something else you need to do once you get that call. Hence there are several, if not numerous, steps that you have to go through to follow through the original call. These are actions that make up a project.

Okay, do the following:

project: Organize the meeting
actions (sequential):
...make call, leave message if needed.
...wait for return call.
...follow through with the call (do whatever needs to be done).

You might place a start date for the first action, if you don't want to do it right away.

Once you make the call, check it off, and the next action (wait) appears in your context view. When the call comes in, check it off, and the third action now appears in context view.