It's very likely that the local telegraph circuit between GCT and MO mentioned by Larry might also be the one that extended to BN. Of course, each office had a plugboard where they could isolate or join circuits, and I don't know if MO had it broken or cut through when I was at BN.
I also remember, about 50 years ago, the communications and signal pole line along the land side of the Hudson Division west of Spuyten Duyvil. It was loaded with about 40-50 communication circuits above the signal circuits, which were many more than were needed to just operate the Hudson Division.
I suspect that most of those were Western Union commercial circuits, telegraph or teletype or both, because up until the late 1940's, I think, the entire telegraph system was owned and maintained by Western Union. The linemen were WU employees who were qualified to operate motor cars on the railroad where they had to. WU handled RR business and maintained the wires in return for occupancy of the RR right of way. RR agents in outlying stations handled WU message traffic and were paid a commission per word and per message.
It is also notable that the Putnam and Upper Harlem Divisions had many more telegraph circuits than their operation would require, probably for the same reason. In fact, it was probably easier to maintain a pole line in some places on the Putnam Division, because of less railroad traffic to contend with. There was also the advantage of redundancy. If a derailment or ice storm took out the wires on one side, they could patch around the other way.
Nowadays, it is common when a railroad grants occupancy to a fiber optic carrier, for the railroad to reserve a big chunk of bandwidh for their own traffic. That's one reason that railroad pole lines are becoming extinct.