We use a corporate chat client. I can usually juggle several simultaneous tasks this way - until someone wants to call me. Phone calls not only monopolize my focus, I'm often less prepared to answer random questions this way as chat allows me the time to log in to the box in question and see what they're seeing. Its easier to answer vague questions like, "Why isn't this working for me?" when I can see what they're trying to do rather than guess.
So often I'll get a chat ping, "Can I call you?" To which I invariably reply, "No." Sometimes they ask me, "Why not?" To which I'll reply, "Why?" They usually cite something too complex to explain without verbalizing it (in which case they just want to vomit words at me - which does not in anyway, do anything remotely helpful), or its "too much" to type - in which case I suggest they may be in the wrong career field by reminding them what it is we do for a living.
Today, however, I got a chat which requested a call citing the former reason. As he talked, I answered every question on chat.