[Grammar] Is it correct to ask, "Who is talking to who?"

[Mike MC]

Is it correct to ask, "Who is talking to who?"
As far as I know, it's ungrammatical because a preposition should be followed by whom: "Who is talking to whom?"
What do you think?

 

[5jj]

I imagine that more native speakers of BrE would use who than whom these days. I no longer consider this ungrammatical.