My favorite is when someone sitting right behind me emails me a question, then turns to tell me they've just emailed me. Moments later they ask if I received the email. As soon as I get the email I notice it's a stupid question that would have taken 2 seconds to ask and even less to answer back.
Both valid points, "chrisgriff" & "almcicoll". However, the REAL reason people do this (PHB included/excluded) is because many (most) people (knuckleheads) have the attention span of gnats (tiny, little insects) and would ignore the voicemail, miss the fax, forget the email, etc, etc, etc.