If Al Qaeda is a foreign power (a substantial if) and if the (let's say) US citizen on the US end of the telecon is conspiring with or a member of Al Qaeda, is that US citizen still a US person for purposes of this statute?
How the court views that is an important question.
Also important, and I don't know the answer, is the fact the language of the statute does not say US Citizen but rather US Person.
Given the fact that constitutional protections have been extended by the courts to non citizens in the US both legally.....
You see where this is headed.
Personally I think this whole problem could be fixed if they just amended the constitution one more time and the amendment simply stated "The above doesn't apply to muslims".