Before revision: MAINWAY is a database maintained by the United States' National Security Agency (NSA) containing metadata for hundreds of billions of telephone calls made through the four largest telephone carriers in the United States : AT&T, SBC, BellSouth (all three now called AT T) and Verizon .
After revision: MAINWAY is a database maintained by the United States' National Security Agency (NSA) containing metadata for hundreds of billions of telephone calls made through the four largest telephone carriers in the United States , including AT&T, SBC, BellSouth (all three now called AT Verizon, and T-Mobile .