My I Ask Who is Calling?

Kate has really been into playing phone. She'll play with just about anything. She has a couple cell phones that used to be ours ages ago but when those can't be found because they are under the couch or in the car, she'll make do with a remote, play car, or any other rectangle-shaped object. Recently Kate and I were having a phone conversation when Christian wandered down the stairs.
Christian (in kind of a whisper): "Who are you talking to?"
Me: "What do you mean?"
Christian: "Who are you are you talking to on the phone?"
Me (pulling away the giant 7" by 5" bright blue electronic device I had up against my ear): "Sweetheart, I'm talking on a calculator."