I have to admit I didn't bother to read the thread. I happened to see the picture in another source.
But, has anybody bothered to explain why anyone would be using the only cellphone in 19-whatever? Who would they be talking to? Wouldn't it be the only cell phone on Earth? As well as being a cell phone without any towers to relay the signal?
As mentioned in the thread, they could be talking across time, to someone in the future, or perhaps another time traveler in that time period. The phone may have the capability to send and receive without cell phone towers, if its a communication device from the future, and it could even do it through time possibly. It could also account why the phone looks bigger than some phones we have now, all the added electronics for this etc....
Your just not thinking 4th dimensionally!