Pros
Good benefits, ample vacation time. You can have a life when you work at AT&T, just don't expect to have an exciting job or many opportunities for advancement. It's also a culture that is not very confrontational, for the most part you don't get screamed at by upper management, they generally are respectful to the employees, at least to their face.
Cons
Getting promoted has become damn near impossible. Poorly performing employees are never terminated, I mean never. The only way anyone is let go is through layoffs and since everyone at the company gets the same exact performance review that process does not have any coherent structure to it. Terrible raises and management makes it clear in many cases that you are nothing more than a number on a spreadsheet.