* This is Tony. I'm Mr. Smith's son.
How do you pronounce 'Smith's son'?
It's difficult to pronounce.
* Hold on a second.
Q1) Is 'for' omitted before 'a second'?
Q2) What is the opposite of 'hold on' in the telephone conversation?
Q3) Can we use 'hang on' instead of 'hold on'? Are both the same?
To pronounce, just ignore the "'s" as if it were written "Smith son."
Q1 depends upon what the rest of the context is. "Hold on for a second?"
Q2 If you don't want someone to "hold on" do you mean "hang up?"
Q3 Either "hang on" which seems slangier than "hold on" or "hold on" but essentially they are the same.
To pronounce "Smith's son," you can break it down into separate sounds: "Smiths" as in "s-m-i-t-h-s" and "son" as in "s-o-n." Say them together smoothly as "Smith's son."
Now, moving on to your other questions:
Q1) No, "for" is not typically omitted before "a second." Saying "for a second" is commonly used to indicate a short period of time.
Q2) The opposite expression of "hold on" in a telephone conversation is "let go" or "hang up." These phrases imply ending the call or releasing the hold or wait.
Q3) Yes, "hang on" can be used interchangeably with "hold on." Both phrases essentially mean the same thing and are often used to ask someone to wait or stay on the line during a conversation.