communications systems from 911 equipment to private telephones cut off by an explosion in downtown Nashville that damaged an AT&T building on Christmas morning.The Dallas-based communications giant said Saturday that two portable cell sites had begun operating in the downtown area, and workers were setting up others in the city and the region."At our facility, the focus of the restoration continues to be getting power to the equipment in a safe and secure way," the company said in a statement on Saturday. "Challenges remain, including a fire which reignited overnight and led to the evacuation of the building."On-site teams working with safety and structural engineers have "drilled access holes into the building and are attempting to.