AT&T have outsourced their IT to IBM for a long time, same as IBM outsources their network admin to AT&T.
The only thing of news here is adding Microsoft to the equation. Anything to do with AT&T is just re-signing/extending of expired contracts.
Seems the only winner here is Microsoft, 3 big US Multinationals, two of which have totally lost any ability to support their own company, and are in a race to the bottom of self-destruction.
If AT&T had any sense, they'd use the opportunity to transition all their IT to Microsoft, and ditch IBM altogether.