Apparently this is a very big deal, because the characters can't stop talking about it 30 years later. Those 30 years go by in the blink of an aurora borealis, which, due to the magnetism it creates in the air, makes communicating over a HAM radio all the more exciting by allowing grown men to talk to their dead pa's. John still lives, by himself, in the family house, which hasn't changed a bit. Otherwise, things are basically the same in both eras. Presto, daddy's on the air.
Problem is, once the characters mess with history, everything goes out of whack.
John really should have paid better attention to the moral of Back to the Future . It's here, about a third of the way into the movie, that Frequency stops being a sappy father-son reunion and becomes a thriller. Genre confusion ensues. Essentially, John feeds his father clues from the case file so that Frank can track down the killer during his original murder spree. As notes and photos in the old file literally evaporate in front of John, he tracks his father's success.