Galaxy Communication's Delta series key system manual and installation guide, 1985. A few of these older systems are still hanging on, but time will come soon when for the need of a replacement. The older Delta phone system was a Key based telephone system. By now you're pushing beyond even a long, long lifecycle. Below you'll find the installation manual for both the Delta 824 and Delta 1232 systems.
Galaxy Communications made these Delta key system phone systems in the 1980s. Perhaps there are still a few in operation.