Nomad Digital's backend is being used, which can take signals from multiple 2G/3G operators to piece together continuous coverage. I imagine the firm uses a virtual network that uses proxies on both ends to allow a continuous IP connection regardless of the intervening network pieces. The user has no awareness of this, and remote sites maintain connections via the proxies.
The service in stations is quite a bit higher, with Pegoraro measuring 3 Mbps/600 Kbps. Regular correspondent Klaus Ernst, an inveterate tester of new Wi-Fi systems around Manhattan, measured 8 Mbps/1.8 Mbps at Penn Station. (Splash screen courtesy Klaus.)
A report from Canada's Globe & Mail indicates that Via Rail's Internet service could use more robustness, where cellular doesn't fully cut it. The firm that operates Via, 21net, only uses cellular connections on the Windsor-to-Quebec City route over which Internet is available. That's what the train operator wants. 21net recommends adding satellite for reliability.
Amtrak Launches Wi-Fi on Acela and in StationsChris Brown praised for picking up rubbish