I know that cellular and WiFi-based systems are two different things, but when it comes to mobile access, they're complementary: cellular (or satellite) provides the backhaul and WiFi provides the last mile (or last 100 feet).

I assumed that if the payment system is based on an IP-based cellular backhaul (i.e. EVDO, EDGE, UMTS), all that would be needed to provide Internet to passengers would be to plug in a wireless access point, and voila (yes, it's slightly more complicated and costly than that, but not much).

I didn't think of the possibility of the train using the radio network. That probably is the most likely possibility, as there are too many areas with spotty or no cell coverage along rail routes (especially where the tracks are away from major highways). If that's the case--or if whatever backhaul they're using isn't IP-based (it may be a proprietary system or might be a direct dial via a wireless CSD/HSCSD modem connection)--then it wouldn't be compatible with a WAP and Internet access

Disregarding the payment system, the poor man's (or poor carrier's) solution to wireless Internet on trains is to get a Sprint or Verizon EVDO card, plug it into a Kyocera KR1 router (which is also an 802.11b base station) and then maybe set up a WDS throughout the train (one access point in each car--the super-poor carrier's solution would be to skip the WDS and only have it available in, say, the lounge car). In the more populated areas/heavily-trafficked highway corridors, I've had no trouble getting 1+mbps off of my EVDO card.

1-1.5mbps isn't a lot to share between a whole train of laptop users (although I would guess that most LD trains would only have a few people on board who would be interested in using the service--unless more businesspeople decide to start using Amtrak because of the availability of WiFi), and if the device falls back to basic 1xRTT (155kbps), things would get even slower. (They could do better by installing a separate EVDO card and KR1 in each car, but that could get cost-prohibitive at $80/month/card plus hardware--although I'm sure Amtrak would get a commercial discount from Sprint or Verizon.)

I've been keeping up on the Capitol Corridor's trials for WiFi service on its trains. There are several proposals for the backhaul link, ranging from WiMax to cellular to satellite. Here's a quote from the CC Web site: "Whether via radio base-stations using linked mesh Wi-Fi, pre-WiMax, or WiMax, 3G, or satellite, or a mixture of these technology solutions, or something none of use have heard about yet, we expect that a vendor may be ready to launch a service in mid-2008." You can also check out the CC's Request for Information. Their list of services the network needs to support include some fairly bandwidth-intensive ones (videoconferencing, CCTV surveillance for Amtrak, and video/audio streaming are the big ones--looks like EVDO's paltry 155kbps upload ain't gonna cut it), so I expect to see a fairly cutting-edge system installed, which, of course, is gonna cost some money. That type of a setup isn't really feasible on a national network. Truthfully, it wouldn't really affect really mobile and Internet-dependent people like me, as we'll simply depend on our own cellular-based services, especially as the prices on them drop.