Do you only get to use 3 killstreak rewards at a time in MW2?

you do and you dont, see you can only choose 3, but say those three are for example mine i choose, i have air drop ( the plane drops off a package ) the harrier ( airstrike with hovering plane that mows down people ) and then emergency air drop ( same as the 1st but with 4 instead of 1 ) now WITH those aird drops it is very possible and quite easy to get 4-5 more kill streak rewards. During one game i had a turret the first got my harrier and after i got my air drop i got another turret, harrier, pavelow and the AC-130... that was a good match lol