('formal') The person to 'whom' we spoke to was very helpful. = ('formal') The person 'whom' we spoke to was very helpful. = (more commonly) The person 'who/that' we spoke to was very helpful.
('formal') Her brother, 'whom' I met last year, is an attorney. = (more commonly) Her brother, 'who' I met last year, is an attorney.
('formal') To 'whom' did you speak? = ('formal') 'Whom' did you speak to? = (more commonly) 'Who' did you speak to?
(..) - Give it back. I'll shut it down if you explain. There's nothing to explain. He's sending letters. Letters? - To whom? - To women, usually. No kidding. Who is it? There's one in particular. El'onore. Who is El'onore? (..)2011 The Intouchables