I have a 683 unit that looks just like the standard 680 except that it has a "do not disturb" toggle switch instead of a volume control. Instead of the modular connector,it has a number of wires ending in spade tips. Does anyone out there have an idea how this could be hooked up? I am pretty sure you could not use an 82 connecting block but what about a 149 connecting block? Was this a special purpose device not actually used with a 4A speakerphone system?