I echo what others have said. It's true that some of the original GTD contexts may become unuseful (is that a word?) with the advent of new technology, but the principle remains the same.
I heard this question in a webinar recently: when you are in a given situation (context), what choices do you WANT to see? If you want to see all ofyour NAs, fine, but if there are situations where you would like a filtered list, then that is a context.
I like digital list managers for this reason. Like MarkDillon, I assign multiple contexts to each NA so that I can custom-filter as needed. For instance, email tasks get a tag of @HomeInside, @Online and @Email. That way, if I'm at home and want to see the full list of choices, I view @HomeInside. If I'm sitting in front of my computer and feel like doing emails I'll just pull up @Email.
However, at work I have pretty much ditched the traditional contexts. I have a desk job and don't travel, so I always have computer, phone, and Internet available. I rarely have more than 12 or so NAs at one time (my work system is separate from my personal life system), so I don't find it overwhelming to see them all at once. I just use consistent verbs to label them, so, when listed alphabetically, similar tasks (e.g. email) appear together.