Re: And another thing...
They're probably targeting this for rural areas who aren't served by cable/DSL currently. Power lines are always above ground in such areas, it is too expensive to bury them.
Likely the "last mile" to the house will be LTE from a fixed antenna on the power pole to a fixed antenna on the house, using one of the bands they own that isn't used for cellular.
In areas where homes already have nearby cell towers that have a fiber connection, AT&T would just add an antenna there and be done with it. But in some areas, due to terrain or low population density, the towers may be spaced too far apart - or be running on a pair of T1s and the cost to run fiber to them is deemed too high. The power line method is presumably a cheaper way of connecting customers in such areas.