The WiFi Rail - BART testing and demonstration period has three phases: 

Phase 1A will provide WiFi access at the following stations:
Embarcadero
Montgomery Street
Powell Street
Civic Center

Phase 1B:
Completion expected by end of June, in the tubes between Civic Center and Powell Street.

Phase 1C:
Complete testing and demo phase by demonstrating terrestrial access at the Hayward Test Track.

Once the completion of the testing has been successful and approved by BART then a system wide deployment may be possible.  Service fees will not be collected and access will remain free until much of the network has been completed.  Initial users of the partial system will be invited to participate in discounted memberships.

The date for testing of services has not yet been set.