Ok. Got a theory on this one. It's probably crap, but I think Alecs is on the right track in his 4th point about a practical joke.
Chaplin was a visionary in many ways. He was at the cutting edge of his particular art.
Is it really so much of a leap of the imagination for a man of Chaplin's ability to see mobile communication as a possibility in a country that already had an established telephone infrastructure? It would also be very Chaplin to hire a drag queen, and then ask him/her to act as though they were talking on a telephone, in the full knowledge that any Chaplin premiere is going to attract media interest, and thus be filmed.
Or is that too fanciful?