The story trumpets wireless, but it ain't Wi-Fi: Underground stations through the Bay Area Rapid Transit (BART) system have had cellular capacity added so that calls and data can be sent. San Francisco stations were first to get the enhancement; more of SF along with Oakland and Berkeley stations will follow. The deal will bring hundreds of thousands of dollars of year to BART's pockets, and eventually millions.
It's interesting that Wi-Fi isn't mentioned as part of this: at the moment, the lowest-hanging fruit is certainly cellular reception. Because this is a deal the cell companies want, it was unlikely to feature Wi-Fi. If San Francisco gets a Wi-Fi network built for it, which seems almost certain at this point, you can imagine that that provider would want to cut a deal with BART, and extra-municipal entity that encompasses a huge part of the Bay and out into what were the hinterlands.