Whom is not calling

The professor in me wants to get this said:

In yesterday’s Newsday Saturday Stumper, the clue “Receptionist’s pronoun” takes the answer WHOM. The answer appears to play on the well-known formula of telephone etiquette: “Whom should I say is calling?” The pronoun who, not whom is what’s appropriate there. I think the puzzle’s constructor, Matthew Sewell, must know that, but not every solver will.

Flipping the sentence arounds makes the right choice clear:

I should say he — not him — is calling.
I should say she — not her — is calling.
I should say they — not them — are calling.
I should say who — not whom — is calling.

“Whom should I say” is a hypercorrection, a mistake that comes about in an effort to avoid a mistake, as when someone says “between you and I” in the mistaken belief that me is always mistaken.

I am trying to remember the last time I spoke to a telephone receptionist. The best I can do is say back in the day.