I worked as a communications tech for ATT from 1972 until 2005. I worked on (in) a 4a long distance switch. There was usually one per city. This was pre computer, all electrical xbar switches. When a call was made and a path
established all signaling and voice used the same path. Blue boxes were a major problem. So much so that ATT completely changed the way things worked. They invented and installed “STP” switches. Signal transfer points. There were now two paths, one for signals (answer, hang up, busy, etc) and another for voice. The blue box would no longer work. Of course this was happening at the same time computing was entering the scene. Once all the switches were 2b computers it pretty much made the issue mute. And our 4A xbar switcher that took up two plus floors of a building (Birmingham, Al) went to a couple racks of equipment in the corner of the room. The blue box helped drive this change. Side note. I tested long distance circuits going out to small cities and towns around the state. If we got tired of waiting for the circuit to become idle we would plug a 2600 tone in, knocking down the call. And yes, some of the guys could whistle a 2600 tone. Fun times.
7 Likes
