: I never got the impression that there was any communication between Denethor and Saruman using the Palantirs. Each seemed to use their seeing stones to gather information on what was going on in the world for their own personal purposes. Denethor was said to be a wise and far seeing man but no one, not even Gandolf, knew of the stone until the pyre.

I don't think there is any direct mention of communication between Denethor and Saruman through the palantiri in LotR. Tolkien does write about such communication in the essay on the palantiri in Unfinished tales however.