I'd go with "I'm Ken. I'm very sorry, but you didn't get the job. I hope you'll consider us in the future."
I don't think most people have a problem with aplication rejection, and they appreciate a call. I don't think anyone even expects a callback, although they certainly hope for the courtesy and get upset if it isn't extended to them.
I'd say you've already covered your bases when you pick up the phone.
