Interesting. I was expecting an article about hooking up two DSU/CSUs together over his own twisted pair wire, and remotely connecting that to his own network. I’ve done that before. For a while at my first job, we had the teleco set up a copper pair between two sites on opposite sides of the city, and had DSU/CSUs on each end. Worked just fine, no ISP needed. Just to be clear, that meant the teleco punched down an existing pair from site A to their CO, cross-connected that to the other CO near site B, and punched that down to an existing pair going into site B. They obviously didn’t need to pull cable for that, nor would they have wanted to do so.
My first employer had their offices, server room, and call center all in one building (a converted strip mall). We had one four-wire T1 from one provider (presumably the first one they ever ordered), plus a fiber “fractional T3” that was demuxed by an Adtran box into a number (single-digit) of additional T1s. A couple of those T1s went to routers where they were the internet link (the office ’net and the servers were just separate VLANs sharing the same uplink until we eventually got business cable for the office), several went to Digium cards on servers running Asterisk (one for the call center and office phones, a couple more for IVR applications), and one went to a SIP gateway that was used for an international calling card service (there was some fun RADIUS stuff involved in that one).