I believe most of the poles are not AT&T's, but rather owned by the county and it's Board of public utilities. The combined power and communication poles have a standard fee for attachment. Google got a special deal to use the power area of the pole for free as part of their enticement. Labor cost is higher for the power area of the pole.

The AT&T deal is probably for just the odd pole where the communications approaches a building from a different path.