It does depend on the situation
I agree, at home callers should identify themselves, and we generally let the answering machine screen calls just for that reason--so few people do that (of course 99% of the calls we get are telemarketers).
At work, 'hello' is not only used to acknowledge the connection but to sound friendly...I work at a small library, so the required spiel is "Hello, this is the City of X Library, I'm Z" with or without a "how may I help you?" (which I usually leave out since getting out all that before the caller speaks is enough of a trick, and I don't know if I can help or not, LOL). The problem is many people will blurt out their name during that, or mumble it and then ask their question, if they say at all, so I am forced to ask again at the point in the conversation when I must have the name (to look up their account, etc.). The rest of the folks assume I should know who they are by the sound of their voice, so I get to feel embarrassed or annoyed when I must ask. I guess I can't win...;-)
When I make a call from work, I always say "Hello, I'm Z from X Library" first thing, to put folks at ease as many are wary senior citizens wondering who on earth knows their name and number...
