AT&T Surplused me at the end of Mar 2019. I've done Project Manager, Product Owner and Scrum Master as well as software test management at AT&T.
Once you move out of technical jobs and into management you get away from the technical deep details of the team. You get the highlights but not the very specific details.
In my job hunt for the PM, PO & SM employers want very technical people. Training for those jobs indicates you are NOT to be technical to the point of a developer or tester. It is just not true, employers want what they want and they want you to be highly technical.
Certifications: AT&T offers their own training and certifications for PO and SM. That may be OK inside the company but I would push AT&T to send you to external training and real Scrum.org certifications. Internal AT&T Certifications mean NOTHING outside the company.
Job security at AT&T..........well there is no such thing. You need to look out for yourself so I suggest you maintain your technical skills and get external certifications as best you can.
Just my 2 cents from my experience.