If a power line is actually involved (looks like just phone from what I can see), DO NOTHING BUT CALL THE POWER COMPANY to deal with it, and DO NOT do any clearance trimming on your own - that's the power company's responsibility, not yours.
If it's just phone as it looks then try calling them, but the phone company will likely just ignore it - I've seen countless phone line runs weighed down with debris and limbs running through the woods practically on the ground and they do nothing until it's physically broken.
If you DO anything that ends up damaging that line you're gonna be held liable, if the tree ends up falling on it's own accord and timing or a storm then it's a natural occurrence.
Finally, you sure that's a Black Walnut? Can't zoom in clearly enough on my phone for a sharp look at the bark, but it sure looks like Ailanthus (Tree of Heaven) from your closer line pics - easy to confuse with BW from a distance or casual look because of large compound leaves in the summer and thick branch tips/very large buds in the winter. Bark is the dead giveaway, as well as the rotten peanut butter stench of the leaflets when crushed up.
