I was watching the Fringe episode, "Peter" (Season 2, Episode 16), where it takes a look at Walter circa 1988, and he demonstrates to a room of military personnel what looks like a Motorola RAZR cellular phone. He mentions that he copied it (I assume by watching it's construction via the "window" device that he had created) from a universe that was roughly 20 years ahead of "us" technologically, and we know that Walter did not visit that universe to get the device, as he clear answers "no" when asked at the briefing at the beginning of the episode (unless he was lying, but there doesn't appear to be any evidence of that.)
But what I don't quite understand, is how he would be able to construct it given the level of technology he had available in the mid-late 80's; the episode takes place in 1988 so he like would have began constructing it some time before hand, at a time when the early IBM PC/XT (Intel 286) computers were still rather new.
So how could such a compact device, especially one known quite well for it's thinness compared to other basic cell phones, be possible to build with existing technology, seeing as phones like the RAZR use much smaller components and chips that weren't around yet?