Originally part of the Tribute to System 75, relocated to a blog post, with an update since it’s original post in 2015.
The System 75 was a fully new system that could handle infinite technologies such as ISDN, PRI, T-1, and later IP and packet switching. At the same time, AT&T also marketed the not so bleeding edge PBX called the System 85, which was a Band-Aid version of the Dimension. But this version would use shared hardware compatibilities with the System 75. In fact the System 85 had some interesting features such as AUDIX “Unified Messaging”, ports could max out to over 30,000 extensions and support up to 40 attendant consoles. Well, not the 302 console I posted earlier, but a boxy one that was used for the Dimension, so boxy it earned the top 6 position as the Ugliest Operator Consoles in 2016 from this site.
Another system called the System 25 was based almost entirely on the Merlin system with the code, and features. The System 25 is much comparable to a Merlin Magix or Legend system of today, which eventually replaced this odd setup.