I'm always amazed at what can surface sometimes on the net to catch our attention and the clip from the movie apparently showing someone using something that looks like a cellphone as they walk along the street is no exception. You can see the clip here Time Travler
And while I don't know about time travel as there are some possible ways it could be achieved but they are all pretty difficult to see ever happening. Of course you only have to look at the PC and the internet to see that amazing things do happen and become everyday events.
But I guess my biggest problem is if this is a person talking on a cell phone who are they talking to and what service provider are they using. Look, face it, there would have been no one else to talk to and no cell phone companies to use back then. So if this person is a time traveler they would have to be using some kind of communication device that would let them talk to someone in the time they came from. Something more like a walkie-talkie or Star Trek tri-corder than a cell phone. So time traveler maybe but they are not talking on a cell phone.