Is That You, John?

graham turner:Is that you, John?
john smith:Yes, speaking.
graham turner:Tell Mary we'll be late for dinner this evening.
john smith:I'm afraid I don't understand.
graham turner:Hasn't Mary told you? She invited Charlotte and me to dinner this evening. I said I would be at your house at six o'clock, but the boss wants me to do some extra work. I'll have to stay at the office. I don't know when I'll finish. Oh, and by the way, my wife wants to know if Mary needs any help.
john smith:I don't know what you're talking about.
graham turner:That is John Smith, isn't it?
john smith:Yes, I'm John Smith.
graham turner:You are John Smith, the engineer, aren't you?
john smith:That's right.
graham turner:You work for the Overseas Engineering Company, don't you?
john smith:No, I don't. I'm John Smith the telephone engineer and I'm repairing your telephone line.