Schau mal unter related discussion im Archiv, ob Dir das weiterhilft ...

I donŽt find any answer to my question there.

Ich zitiere hiermit Mr. Bs Antwort etwas umformatiert:

<Zitat>
As a theoretical rule:
In positive statements you use "some", in negative sentences and questions you use "any".
"Is anyone there?" "No there isn't anybody"
"Do you know anyone from India?" "I don't know anybody who lives in India now, but I do know someone who used to live there."

Same with any/some otherwise:
The question "would you like any tea?" is a neutral yes/no question. But "Would you like some tea?" is an offer.
This rule is however broken so much of the time, that it is more just a guideline until you're sure what you're doing.
</Zitat>

Nun auf Deine Frage uebertragen:
"Is anybody here?" Offene Frage, der Laerm kann auch von einem Haustier verursacht sein. (Rainers Eselsbruecke "Ist irgendjemand hier?")
"Is somebody here?" Du weisst bereits, wer den Laerm verursacht hat. (Rainers Eselsbruecke "Ist jemand hier?")

Habe ich das so richtig verstanden:

Wenn ich einen Raum betrete und niemanden sehe, dann frage ich 'Ist da jemand?' mit anybody.

Wenn ich meiner Freundin etwas vorbeibringen möchte, dann frage ich (am Telephon) 'Wird jemand daheim sein?' mit somebody.

@Selima:
offene Frage mit any
geschlossene, nicht negierte Frage mit some

=> Du gehst davon aus, dass sie daheim sein wird, und willst Dich nur dessen versichern: some - There will be somebody at home?
Du weisst nicht, ob sie daheim sein wird: any - Will there be anybody at home?

When I'm the last one out of my workplace, before arming the security system I call out, "Is anybody here?"

I don't really know the answer, but I don't expect a positive answer.

When would I expect a postive answer? If I hear people talking. In that case of course, you wouldn't even ask.

What if I'm not sure? Thought I heard some papers shuffling, or maybe a pencil drop several offices away, and it seems that someone is here, but I'm not really sure. Then I might ask, "Is [there] somebody here?" But even in this case, you could still say "anybody".

There is another difference that I feel, and that is that "anybody" is more anonymous than "somebody". Suppose you live with several people and you wake up in the middle of the night and go downstairs for a drink. You're see a light on in the library, and you hear what sounds like pages turning, but you could be mistaken.

You woudn't say, "Is anybody there?" because it can't be just anybody, it has to be one of the few people who live with you. So, you say "Is somebody there?" (In reality in that situation, if I had any clue at all who the most likely choice was, I would probably name them: "Joan, is that you?" --knowing that Joan has a test tomorrow.)