Ah, John. You must be referring to the Carterphone. This was a speakerphone unit that was self-contained but it connected to the network through a cradle that held the telco-owned phone handset. It wasn't legal to physically wire CPE to the network, so this speakerphone was acoustically-coupled to the standard phone.
Bell companies tried to argue that this was an unauthorized attachment, just like the old vinyl covers for the phone books full of funeral home, gas station and fuel oil company ads, but the court threw it out. This led to a ruling that allowed customers to physically wire privately-owned equipment to the network (through a registered jack and appropriate coupler). Am I on the right track?
Am I right? What do I win? I'll take one of those nice Sundance Communications shirts.
On the other subject about the couplers to "protect the network", they were a true PIA since they were chock full of fuses with plain stupid ratings. A simple slip with a butt set resulted in a call to the telco's repair service. God forbid we go into their coupler (I think it was called a registered coupler) to replace a fuse. To make matters worse, I swear that the monthly rental for these things made it difficult to justify customers buying their own systems.
The telcos protected themselves by using 74- type fuses so they could tell if "the enemy" replaced them. Back then, you couldn't buy these fuses on the private market. They were Bell-controlled and only made by Western Electric. The truly weird ones had colored-tips like red/white that represented some crazy amperage, like .0075 amps! (No corrections needed; it's just an exaggeration).
I will never forget when I was a Jeff Moss type of guy, helping out at my dad's real estate office and trying to learn. I decided to clean up some of the sloppy workmanship in the telco's building entrance terminal. I was using simple scrap pieces of jumper wire off the floor to lace up the mess a little bit. I went to cut the ends from my tie wire and accidentally clipped the T/R of the company's second line. I quickly twisted the pairs back together (and learned about ringing voltage), but by then, I had blown the talk battery fuse in the "coupler". For two days, the busiest real estate office in town operated on one line since NJ Bell wasn't about to come running for one of "those" customers!
I hate to think of how these things did after thunderstorms with sensitivity like that.
