When telephones were the cutting-edge of technology, cheap knockoffs arose. This Radio-Shack-style wired intercom sought to cash in on Ma Bell's high standards. Imagine stringing one mile of wire from your house to your friend's home through the neighborhood.
There are several sets for sale on eBay as I post.
There are some very specific things you shouldn't say to your co-workers. Offensive things. Questions and comments that could lead to a lawsuit, or getting fired. But how do you know exactly what those things are? Aside from using your common sense, the Delaware Department of Transportation was kind enough to make this brochure. They also issued an apology when, surprise!, people found the brochure to be offensive.