This device allowed you to use 3 devices on the same single phone line to the home or office. 2 of the ports are linked, so it can switch between 2 devices such as a phone and modem, the extra linked port can be used for a fax machine or answering machine.
The company Command Communications started their business in the 1980s but closed all operations in 2011. They made products such as phone line sharing devices, paging systems, HDMI switches, and fax line switches.
I found a device very much like the one I pictured here when I was a kid at a thrift store. I added it to my modem to see what it did. I was able to dial onto the internet and everything was fine. Then I heard the phone ringing… I was expecting my computer to go offline, but instead it was just paused. I had never seen the internet do that. Then when my mom was done with her phone call and hung up, the internet continued working. It was life changing for us. I could be online all the time, and my mom would not miss any calls.