You might consider a used multi line phone system. You can pick up something like an intertel GLX system on Ebay for a few hundred dollars, and that gives you 12 possible telephone extensions, up to 6 phone lines, loudspeaker, paging, etc all in one lump. Put an extension in every room in the house and every building and one button pages them all, or you can reach just one extension from any other extension. I have the GLX in my shop and office, requires only a 6 conductor wire to each jack. I put it in new, and it's obsolete now, but I just buy hardware on ebay when I need it.
