At first glance there is nothing terribly unusual about this cover. The Wirt Roland design was commissioned by AT&T first for its Detroit Telephone Company, then used across the entire 'Bell System' and even in many locations around the world. However AT&T never really dirtied its hands with man-hole covers, that was the job for the hundreds of independently owned telephone companies, In Manhattan and the Bronx, the dirty parts were placed and repaired by the mysterious Empire City Subway Co. Limited (a wholly owned subsidiary of AT&T) Even the lettering on this cover seems a bit ad hoc. And yet it exists!
The design is the classic Wirt Roland double ring of hexagon. In this case the variety where the outermost hexagons remain separated from the outer ring. The center badge has somewhat pointed looking sprokets-like extensions around a circal enclosing an outline of the Bell System bell and the rather spindly letter uneasily set around it.
Undoubtably for Telephone & telegraph wires, and fiber cable today too.
There are thousand of Wirt Roland designed covers in NY. This is the only cover of any design with the lettering AT & T.