Hello!
I am from Germany and I don't know about them. Here ISDN terminators (called NTBA) are mounted inside. They had the 2-wire Uk0 Bus at the carriers side and the S0 bus on the customers side and were connected to the TAE telephone socket, so no technician needed to come home when ISDN was ordered.
What are exactly these ISDN boxes referred in the article? What came out at the customers side? An S0 bus or something else?