Most utility companies in the US will come out and cut it all off of the pole if they see it, or if someone else sees it and calls it in. It's actually trespassing. Utility companies have easements, and the poles belong to them. People often build fences, buildings, etc. around the poles, and many utility companies tolerate it as long as they can still access the pole. If the poles aren't actually being used, anymore, you can go to the courthouse or city offices and try to find out which utility company owns the pole (can be power or telecom) and ask them if they will abandon the pole. Older poles, they usually will. Newer ones, they may just come out and remove it.
If the pole has telecom or power lines still on it that are being used, it is very unlikely that they will allow a zipline connection to the pole. I sometimes seek permission to attach wire ham radio antennas to them, and often they will let me do this as long as I make the end of the antenna connection with a hook or snap, and use a screweye on the pole so that their workers can disconnect it and drop it into the yard. Sometimes, though, they say no... they will cut off anything on their poles.
When I did get permission, I showed them my past work record with utility and telecom companies, and assured them I wouldn't use a ladder.
Still, a zipline has human beings attached to them. I seriously doubt if they would give permission for attaching one to their poles.
