I had one of those between my home and my office. It worked great for about 6 months until it stopped working entirely. No support was available because the only supported signaling was the closing of a relay. The phone company seemed to be searching out likely alarm circuit data use and putting filters on them to force an upgrade to a data circuit. (USWest/QWest)
Didn't see the same with SBC/ATT [1] in the Chicago burbs mid 90s fortunately. Even got a tour of the central office by walking up to the door as an early teen and asking to look around. Different times.
There were a couple of us around here who had the alarm circuit hack for DSL until Bellsouth finally figured out how to make it impossible to order. It was never easy, but (I assume) neglect of the systems, changes in tariffing and oversight, and BS not wanting to sell it finally let them get away with not provisioning the service without explicitly saying 'no'.