Strangely, my ear is mixed on this. When someone calls on the phone and
asks for Mr. Whicker or John, I always answer "This is he."
But, when called on a roll, I usually answer, "That's me." In
both cases, the alternative sounds wrong. I can't say "This is him" nor "That's
I". As for "It is I", I never use either; when asked "who's there?" I usually
answer with my name.
I found it interesting that people were throwing around the word "correct"
regarding this issue. It was interesting to think that I might be corrected for
answering "This is he" because it has become incorrect to use the nominative for
subject complements.
John H. Whicker