I've never found a truly satisfactory solution for modelling telephone/telegraph/power lines, due to the fact that the prototype lines sag in cantenary loops. Trying to get that right is almost impossible, although it might be done using very thin strands of wire. High voltage lines, OTOH, are generally tight between supporting poles (hence the term "high tension lines". The other problem that comes up sometimes with adding wire to your poles is the possibility of snagging them if you need to reach beyond them on the layout. Thusfar, on my own layout, I haven't strung any wires, even between the high voltage towers, and have avoided putting up telephone poles...sofar.