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Fluke makes a bunch of tone generators and circuit finders that you can use to figure out which line you need to work on. I assume linesmen have something similar for their more robust needs.
Power linemen have phasing sticks to determine which phase is which.
Datacom wires are, to start, much lower on the pole than power cables, and have markings on the cable jacket to determine what the cable actually is (fiber, coax, tel, etc). Beyond that, there is usually some tagging at each service point.