Wired up to----

I notice so many telephone lines (I assume that they are telephone wires) going to so many neighbouring houses and wonder as to how many are actually being used. I have one, but I have cable which is situated under ground so mine is not being used and has not for almost 15 years.. So many homes don't have a landline ,so how many of these are redundant???  The burning question therefore is- why are they still up there.?? Maybe the bird knows??