The disruption kept mobile phones and computers offline in a transit system used by one of the most wired cities in North America. Riders couldn't make wireless calls, surf the Web or dial 911.

One commuter, a San Francisco quality assurance engineer who asked that he be identified only by his , said his phone service was cut around 4:10 p.m. as he headed out of San Francisco's Montgomery Street station on an underground train bound for West Oakland. "I noticed other riders looking quizzically at their phones as well," he said via e-mail. His T-Mobile service vanished until the train emerged above ground several miles away in Oakland, he said.

With all services cut, Greggawatt was concerned that he wouldn't have been able to call police or the fire department in the event of an emergency. "Shutting down 911 service was extremely irresponsible," he said.

The Bay Area Rapid Transit (BART) District said Friday that it cut phone services out of safety concerns. "Organizers planning to disrupt BART service on August 11, 2011 stated they would use mobile devices to coordinate their disruptive activities and communicate about the location and number of BART Police," BART said in a . "A civil disturbance during commute times at busy downtown San Francisco stations could lead to platform overcrowding and unsafe conditions for BART customers, employees and demonstrators."

On Friday BART initially claimed that it had asked carriers to cut service Thursday night. A few hours later, it changed a statement on its website, saying that it had cut services itself.