The eastern US gaps on the Verizon map correspond with population gaps, so I don't see what the problem is. A good example in the Verizon map is northern Maine. Most of that area is underpopulated and privately owned by paper/logging companies. You can't even drive there without authorization, and the roads you do drive in are mostly dirt tracks dominating by logging trucks. For northern New York, the main gap looks like the Adirondack area, again pretty underpopulated. Likewise for the NH and VT gaps. So you can't assume that all of the eastern US is part of the Megalopolis. There is some space left!

On the Acela ("high" speed train that runs up and down the Northeast Corridor), they have a quiet car. I was traveling back from Philly and just after New York some guy enters the car blathering on his cell. Approximately 2 seconds later he was forced into a different car (there are doors between cars). So we have this in the US as well.