Though you may have found some free wi-fi in BART stations and on some trains the last few years, the test program under which that was being provided has now ended. As BART spokesman Jim Allison said in a statement issued this afternoon, "BART has terminated its License Agreement with WiFi Rail, Inc. (WFR)," adding that WFR service had only been offered in downtown San Francisco and Oakland and on about 5% of the train fleet. The trial program may be over, but SFist asked Allison why the contract was terminated, and this is what he said.
WiFi Rail, Inc. (WFR) offered service on a free test basis for several years in limited areas and the test concluded.
WFR has not submitted an adequate financial or technical plan for completing the network throughout the BART system. Also, the performance of the constructed portions of the network did not meet expectations.
38 of BART's 669 car fleet were equipped; also, service was available at some stations.
Going back to January 2013 BART was sounding some alarm bells about WFR, saying they were having "trouble coming up with the capital needed to fulfill the contract" and noting riders' dissatisfaction with the weak signal and connection charges they were being asked to pay. The WFR contract dates back to 2009 and was at the time billed as a 20-year agreement, as Bay City News points out.
Cell service in some stations, which dates back to 2009, will not be affected. But it seems like this might affect some of your connectivity in downtown BART and Muni stations where you may have been relying on this free wi-fi without realizing it. BART says it is "working to have mobile phone service throughout the remainder of our tunnels and underground stations, including those in Berkeley and on the Peninsula," but that won't be completed for a while.
Best of luck getting those emails out.
Update: Sacramento-based WiFi Rail is now threatening to sue saying that BART is illegally backing out of a contract. As WFR's CEO Cooper Lee tells the Chronicle, "The principal issue was trying to expand coverage, but they’ve been consistently blocking our ability to do so... The contract we have with them says that they are to let us know of any bad service and we correct it within 30 days. They haven’t done that. Instead they canceled what was supposed to be a 20-year contract with no just cause."