It all depends on where you work and which company you came from before the mergers
Pros
In reading all of the reviews for AT&T, I see a wide range of pros and cons. This is because AT&T consists of a number of merged companies which had different work sites, policies and cultures. A reviewer's opinion of AT&T depends upon where they work and which merged company he/she worked for. I see lots of complaints about not being allowed to telecommute. However, I telecommute most days and know of many people at my work location who telecommute occasionally or often. Other complaints center on benefits, but again it depends upon what your benefits were in the pre-merged company vs. the benefits after merging with AT&T. Maybe in 10 years AT&T will have a consistent corporate feel across all locations and organizations, but that's not the case today. I feel that the pay and benefits are good reasons to work at AT&T.
Cons
The downside is that you may end up working for an AT&T organization in a location with poor morale, micromanagement, employee distrust, etc. Also, AT&T is constantly cutting, cutting, cutting, and looking for ways to save money. This often ends up reducing benefits for employees. Regardless of whether or not the benefits are better than industry standards, the reductions result in less of what you had before.