Cell Phone Moral Dilemma

So I use a cell phone as my only phone... I have no land-line. To you city folk this probably seems pretty normal but here in Vermont its still a fairly novel idea. So of course it has caller ID and all that. I'm realizing that cell phones are changing forever the way we answer phones. It used to be "hello?". Now its "hi, so-and-so". But I find that when I answer that way, the person calling is like "um, oh, uh, hi! Um, this is so-and-so. Um, oh, but I guess you knew that. Um, well, I was just calling about...". They are taken so aback by it. So I often just say "hello" even though I know who it is, so they can think they're having their customary 5 seconds of anonymity, and then I pretend to be surprised when they tell me who they are. Recently I've modified this slightly where I'll answer "hi, so-and-so" if I happen to know they are a frequent cell phone user. So... is this right? Does this fall under lying? dunno. All for now...