my grandparents have just purchased DSL and are attempting to set it up without my help. So I am asking those with DSL (they have verizon), the package includes 5 DSL filters, do you use them on all your phones/accessories or just the one plugged in via the splitter for the DSL modem? I have cable so I don't know as much about DSL and can't see the package to tell them what to do.