It sure was a lot of fun to think about the possibility that the Charlie Chaplin time travel mystery was indeed, a person from the future talking on a cell phone, but the video below pretty much proves that this is nothing more than someone using a Siemens 1924 hearing aid.
The Siemens 1924 hearing aid was a pocket-sized, rectangle-shaped hearing amplifier, which transmitted current across a carbon-granule chamber to a vibrating diaphragm electrode. The vibrations from the device were then transmitted to the ear as sound.
The person using the hearing aid would hold the hearing device up to his/her ear to use it. If you watch the video below, you can see that the man using the Siemens 1924 hearing aid has his knuckles curled up in an identical manner to the mysterious person on the Charlie Chaplin time travel video. It almost appears that he is holding a cell phone, doesn’t it?