You don't want to run 70volts paging through the same cable as the phone (it will bleed through).
Either put another amp in the other building and feed it with a 600 ohm source (off of your PBX or key system) or if you've just got one or two speakers there run an output off the amp through the telephone cable. Use 8 ohm/70volt transformers at each end. Step it down to 8 ohms going in to the pipe and step it to back up to 70 volts when it come out.
Sam
