Momentarily, derived from "momentary," has primarily been used to mean "for a moment" ("the sensation is momentary," therefore "the sensation will last momentarily").
However, it's also commonly used to mean "in a moment," as in "she'll be with you momentarily."
I've heard that called a misuse. I'm not sure when it happened, but Oxford now lists that second usage with no qualification except "North American."
I observe that North Americans use it regularly, and I've just noticed it in an old Columbo episode, so it can't be new. Personally, I've weaned myself from it, preferring "shortly," or "soon," or "in a moment," or even "presently" (which deserves its own post).
Does using "momentarily" to mean "soon" sound "wrong" to people on other continents?