Problem: A decrease in stockholder equity is not necessarily a bad thing. It really depends on the cause of it. According to my text cumulative effect of the declaration and payment of a cash dividend on a company's financial statements is to decrease both stockholders' equity and total assets" (p. 549). If this is the cause then it could be a good sign that company is still paying dividends in a recession. However, I do not believe AT&T is in trouble considering the success of their 4G network. While I am not super familiar with the company's finances I do not believe they are losing money because there have been no major announcements about it, like when someone such as Best Buy posts a loss. Since you are a little more familiar was it clear what caused the loss?
https://phx.corporate-ir.net/phoenix.zhtml?c=113088&p=irol-sec&control_selectgroup=Annual%20Filings (dated 02/04/2012)