Pros
AT&T is a leading edge company with a long history, stability and growth potential. Because of the size and scope of the company, there are lots of opportunities for vertical and horizontal movement, and you will find yourself working on projects and learning about things you never dreamed you would be! It's not "the telephone company" anymore!!! There are opportunities in areas as diverse as network engineering and IT, entertainment and content, sales and marketing, legal, finance, HR...you name it. Because of the nature of today's telecom marketplace, I would expect applicants with experience in customer lifecycle management, product lifecycle management, entertainment and content, and IT (particulary IP) would have better than average opportunities.
Cons
I really cannot think of a downside for the non-hourly employee. However, I hear a lot of complaints from friends who work in union-represented positions. Still, positives outweigh the negatives. Complaints are mostly from sales and support (customer care) positions, complaining of long hours, little recognition (though great pay), poor managers, and little opportunity for advancement.