Thanks, Casiopea .
My teacher told me that occupied is right, while engaged isn't used for it, but I watched a movie and I saw "engaged" in it. So, it's used too, probably. However, I need some glasses perhaps... That is why I rather asked you.
'Engaged' is traditional English. 'Occupied' is more universal and probably taken from American English. In public toilets in England you will often see 'engaged' on the door, although this is now more likely to be a red sign for engaged or occupied and green for free or unoccupied. So both are correct and acceptable.
And what about the following dialog? Could I use also "occupied"?
A: Could I have extension 2387, please?
B: I'm afraid the line's engaged at the moment. Do you want to hold?
B:I''m afraid the line is busy, not occupied or engaged- meaning that someone else is using the line, calling or maybe the phone is off the hook.
In many occasion what we used in dialogue is I am very busy, I can't talk right now.
You can say I am engaged in a commitment, I am engaged to be marry.
Hope you can see it better
I'm sorry what does first sentence even mean? What does A want from B? What do you mean by extension 2387?
A is making a call to a company or large building with many extensions to the main external number. Having reached the switchboard operator (B) A is requesting to speak to someone located at extension 2387. Unfortunately the person at extension 2387 is speaking on the phone, therefore it is not possible to connect. B is explaining this fact to A and asking if A wishes to 'hold' or wait until the line is cleared.