I think nested contexts are too hierarchical and I believe you can accomplish the same basic functionality using regular old folders. I have a home and work folder and have calls in both. When I'm at work I simply focus on the work folder and then when in the context view I only see work related calls. You might try this and see if you get what you want. An alternative (I believe the demo vid uses this) is to fake it out by using contexts such as Home:Calls and Work:Calls. I don't personally like this approach, but whatever works for you.