I can confirm that this is an AT&T building. I don't know if this is a data center or transfer center or what happens there though. This building style is very common in large city AT&T buildings. Smaller cities have basically small windowless fortresses- they definitely dont want anyone seeing inside. And many of their buildings are mostly empty now as the buildings are old and the tech over the years has shrunk significantly in size. Lots of creepy dark empty rooms and peeling paint and out dated equipment being VERY slowly modernized.

I do not work for AT&T but I evaluate aspect part of many of their buildings across the US. They are a very bureaucratic company and very compartmentalized.