MetroPCS, AT&T, Sprint, T-Mobile and Verizon all provide mobile services on BART. BART didn't respond to messages asking how long the disruption lasted.

A San Francisco spokeswoman for Sprint said that her company is investigating, but she said that BART did not inform her of the service cuts. "I learned about it through the news," said Caroline Semerdjian. Representatives with the other carriers could not immediately be reached for comment.

The transit agency has weathered criticism and protests for the past month, ever since a BART police officer shot and killed 45-year-old Charles Hill on a station platform. BART, which maintains its own police force, said Hill had thrown a knife at the policeman right before he was shot. It's the second fatal shooting by BART police since 2009. Last year former BART police Officer Johannes Mehserle was convicted of killing an unarmed passenger, Oscar Grant, while making arrests after 2009 New Year's Eve celebrations got out of hand on BART's lines.

Protesters had shut down BART during a July 11 protest over the Charles Hill shooting, but were apparently trying to mobilize the Thursday event at the last minute in order to retain the element of surprise. By cutting mobile service, BART thought it would prevent this from happening,

Mobile phones and Internet services such as Facebook and Twitter have been lauded for helping protesters organize uprisings in Africa and the Middle East, but when they're used for the same activities closer to home, U.S. and U.K. authorities are still figuring out what to do.