Who is on the line?

Who is on the line?

Who is on the other end of the telephone? A: "Who was that on the line, John?" B: "Oh, it was just some solicitor trying to sell me life insurance." A: "Who's on the line, Mommy?" B: "It's Mommy's doctor, so it's very important that I hear what she's trying to say."
See also: on, who