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.
Delta 824-1232 User Guide & Installation Manual
Galaxy Communications made these Delta key system phone systems in the 1980s. Perhaps there are still a few in operation.