***** NOT A TEACHER *****
Hello, Guillaume:
I think that many people here in the United States also say "Hold on."
Personally, I think that it is very rude and that it should never be used.
Maybe I am imagining it, but its use seems to be decreasing.
On the other hand, when I call a company, the busy receptionist who answers might ask: "Can you hold?" At least that is
a question, not a curt order as is "Hold on!"