Janzen Electronics.  http://individual.utoronto.ca/janzen/electronics

ACC Network

The ACC (Audio Cable Communications) network is a new type of intercom system which allows separate modules to be connected by means of phone jacks. Each module or "transciever" allows both voice transfer and a "call" signal, which may result in a ringing bell or a flashing light. All connections can be made by 4-wire phone cable, which allows the use of two separate channels. Some transcievers can switch between the two channels, while others are hard-wired for only one channel.