Ok, but how would you use it? When you access the port via *70, you initiate a single direction page. If you picked up an extension in calling group 1, you'd be in a private intercom call between the two, no longer a page. If the talkback acted as an intercom, wouldn't it trip to an intercom call? If it didn't, wouldn't noise or conversations from the talkback areas enter any page made? Of course, I don't think volume on talkback circuits is nearly sufficient to overpower a PagePac.
Color me confused as to how it could work?