Wow, I'm really surprised with the quantity and quality of responses to my initial post.
I suppose the concept that helped me the most from the response is to be creative about the use of contexts and to allow the contexts to be fluid.
There don't have to be 3 or 4 standard contexts (@office, @calls), but you can change the context to meet your current needs, and have relatively ad hoc contexts, adding one when need for a particular project, dropping it when the project is over.
So now I know what my next level of implementation of GTD is. I just finished my first year, and understand that it takes two years to really get this. I was starting to feel I had nothing left to learn. . . usually a sign of complacency rather than competency!