Pros
AT&T is an industry leader. They are trying to remain on the cutting edge technology wise, by providing the most exciting, in demand products for customers. The fact that AT&T is a large multistate company means there are 1000's of employees country/worldwide. I started working for the company when it was still BellSouth. A lot has changed since that transaction took place in the mid 2000's.
Cons
AT&T in it's current incarnation is all about the bottom line. I worked in the wireline division. My office was closed. I am unable to find a job within AT&T. There have been several layoffs in recent years. AT&T doesn't seem to want to retain their talent and help place the employees in there growing areas. They cast their tenured employees aside. They hire people off the street and in retail and pay lower salaries. The only way you seem to be able to get a job or promotion (internally) is if you know someone in the hiring capacity who is willing to hire you.