Pros
I think the AT&T tries to pay you what you are worth. If you are modest or not a good salary negotiator, you will still get raises. As the company transforms itself to a software company, they have finally made technical training available to employees. Before that, I always had to find ways of training myself in order to keep up with technology.
Cons
The work is often stressful. During the 3G and LTE coverage races, employees were often exceedingly high workloads. My group was often understaffed. In the last 5 of the the 15 yrs that I was at AT&T (mobility) an emphasis was put on cost cutting, and cycle time reduction. We had to write SMART goals that would be reviewed in our A&D meeting with our supervisor. These goals had to include cost saving and cycle time reduction metrics. As an engineer, I did not always feel like I had control of these aspects of the job.