From answering machines, "I'm not here right now..." Well, when and where are you, then? And you'd better arrive in the here and now as soon as you can, because here and now are all there is.

OTOH, what they really mean is too cumbersome to say, along the lines of "I won't be here when you call, which is now for you as you hear this but later for me as I'm saying this, because if I were to be here you wouldn't be hearing this message, which you evidently are..."