Must have been before voice changing software. You would be surprised to find how many CEOs (Chief Everything Officers) answer in a different voice and transfer the call to themselves if it's someone they want to talk to.
I knew a radio DJ that worked at two sister stations under different on air names. One night the DJ that worked at the sister station in his time slot called in sick. He had to run both stations at the same time, running from booth to booth. It was fun hearing him trying to remember which station he was on and correcting himself after starting to use the wrong name or station ID.