Most everyone uses "voilà" [vwa la] at some point in her life. This is likely because voilà [vwa la] is a French word. We Americans like borrowing things from the French. They are just so fashionable.
Voilà [vwa la] has all the expected subtleties in its native form, but we barking Anglophones tend to use it to mean, "Ta da!" This is a fine usage, given that voilà [vwa la] could be translated to mean, "lookit!" or, "here it is!" So carry on, friends. Carry on.
But do not ever spell it "walla" or I will laugh at you.