Between Boston, NYC, and DC, Amtrak runs the really fast Acela trains, the pretty fast Metroliners, and the slower local trains. There's also lots of commuter train service in the Northeast that isn't Amtrak, such as New Jersey Transit, the Long Island Railroad, SEPTA, DC Metro, etc. Back in the 1980s and early 90s I used to take the trains from New Jersey to DC (before the Acela started, so Metroliner if I could, or the slow trains otherwise.) Depending on where I was going in DC, it was often faster to take the train, because there's a lot less "hurry up and wait" and the train stations were more centrally located.
Outside the northeast, Amtrak runs passenger service, mostly long-haul, with occasional shorter-distance service like the trains from San Francisco Bay Area up to Sacramento and Lake Tahoe. That service runs on the same rails that carry freight trains, and freight has higher priority, so sometimes the passenger trains have to wait. I've never been on one that mixed passengers and freight, but I suppose it's possible that they're doing some of that these days.
Back when I was taking the trains, Wifi hadn't been invented, most people didn't have cell phones, and cell phones mainly worked near the city; there was a big service gap between Baltimore and Philly. I was once in one of the dining cars, and the old guy sitting across from me had the smallest cellphone I'd ever seen (a Motorola flip-phone analog), the smallest laptop I'd ever seen (a 6-pound IBM model you could only get in Japan), and an alphanumeric Skytel pager (which was also cool.) He was Professor Dave Farber, then of UPenn, and he'd just been working on the EFF founding :-)