Forum:Modern Warfare 2 Kill Streak question

Okay, So: I dont want to seem like a dumb-ass, but this has been bothering me for a while now; In MW2, there are some kill streak rewards that are on the same number of kills. Is this just the "Customizable Kill Streaks!" thing, or do you get one after another? I think the first is more logical, but i am not sure. While we are on this subject, i would also like to know if, say, for example: I have a 4 kill streak. I walk in a room and see 3 people, and i kill them all. I go to call in my air strike, but find that my helicopter has overridden it. Will this happen in MW2? It seems like Infinity Ward should have fixed this, especially since the kill streak rewards are much closer together now. Thank you.