[pronoya]

I think the confusion also lies in the assignment of a context. If you're following GTD concepts, it really is about assigning one task to one context. In your milk example, these are really three separate tasks. Really, the order is

Discuss with wife who should pick up milk : context (home) or phone

The result of the discussion determines the next task, if any. That is, if your wife is picking up the milk, you're done.

I'm not so much telling you how to buy milk here. Rather, I have found that projects can and MUST be broken down to their next physical actions. When we get down to this level, assigning contexts becomes intuitive.

Just my thoughts...

Daniel