A recent trend, one that was particularly prominent in New York, is to use the word momentarily to mean “in a moment”. I’ve always frowned upon this use, believing it to instead mean “for a moment”.
So my view is that the former of the uses is correct, while the latter is wrong:
- She muted the call momentarily to cough up a lung
- I’m just going to mute the call to cough up a lung, but will be with you momentarily
Answers.com seems to ratify my view.