Who's on the phone?

Who's on the phone?

 and Who's on the line?
Who is on the telephone line now?; Who just called on the telephone? (The caller may still be waiting.) Bill was on the telephone, and Mary walked by. "Who's on the phone?" asked Mary, hoping the call was for her. Tom asked, "Who's on the line?" Mary covered the receiver and said, "None of your business!"
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