It would be proper... if it fits the sentence.
(In your mentioned case it does)
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It all depends on who you're referring to. Not a name, but whether it's "they" or "them" that would fit in the phrase.
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Example of "whom":
"Whom did you call?"
If you rephrased the sentence, "them" would fit in there, hence why "whom" is used.
"Did you call them?"
This works because "they" did not call your friend, your friend called "them"
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This is generally the law ⇣
Who - They
Whom - Them
The main reason people say "who" so much is just society, but most of the time it's correct anyway.
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Good luck! :)
~pinetree