See the young time traveller using an iPhone at 1:00 in this Pathé story about the proclamation of the Dogma of the Assumption on November 1st 1950.
THE ASSUMPTION PROCLAMATION
This is NOTHING like that other film from January 1928 at the premiere of a Charlie Chaplin film, showing a woman supposedly talking on a mobile telephone. There weren't any mobile phone towers back then. Obviously it is not proof of time travel. But you can use the camera function on an iPhone without needing the 3G to be working.
UPDATE: Apparently this woman visited the 1940s first.