Speaking of the 4A speakerphones.... In AT&T's headquarters we had mostly 4As in small conference rooms. But the problem was "mute" would only mute as long as you held the button down. The ingenious solution was while holding the button down, slide a penny between the button and outer shell. Perfect thickness to keep the button down! Of course, before the first year of Divestiture was even over, the New Jersey Bell Centrex was removed, and replaced by a System 85 (1A2 equipment & phones were hauled out by the dumpster). The mute on the new voice terminals was toggled on and off, saving meeting participants money!