Most of the electro-pnuematic braking systems used on transit equipment (subways, light rail/streetcars, etc.) and some commuter and intercity trainsets have ABS capability or something like it, and the electronically controlled pneumatic braking (or ECP braking) systems that NS and other railroads are testing may have something like an ABS feature as well. (It's likely not going to be true ABS, though, as that requires being able to monitor wheelslip on some or all wheelsets of the individual cars, which the ECP systems in testing probably don't provide for and would require fitting speed sensors onto each car; I'm not sure freight railroads or car fleet owners/lessors would want to spend that much additional money on top of adding ECP, but Amtrak and other passenger operators might. We shall see...) Some of the newer locomotives may have an ABS function built into the independent (locomotive) braking system, but I doubt it, since there's probably not much need for it when running light.
Keep in mind that ABS requires both electronic controls and a braking system that can be precisely controlled. Most modern types of transit equipment, passenger trainsets (HSR and otherwise), and EMU/DMU railcars have that or have been refitted with it; conventional locomotive-hauled trains using standard air or vacuum brakes don't (ECP may change that, though, depending on how it's implemented and what systems are used).
