I'd never seen these channels until you mentioned it.

There are two poles like that on the block where I live. They're obviously new, judging from the soil pile where the bottom edge goes in.

The poles themselves are heavily scarred with spike marks. These poles have been climbed many times by linemen. I can't remember when I last saw someone climb a pole, everybody uses a bucket truck now. I don't know if they even train people to do it anymore. I imagine the oldtimers could tell some stories about it. At any rate, that probably says something about the age of the poles. I wonder if the spike marks increase the decay rate of the poles.