It's never supportable as it is what it is. What's stopping you?
I would like to extend my ethernet network to my shop which is located approximately 400 feet from my house. Burying new cable would be difficult due to paved driveways and other obstructions but I have an existing unused phone line buried to the shop. This is (presumably) a high quality cable installed by the phone company to provide service to my home and is no longer used so I am wondering if I can convert it to use as a network cable? I believe the cable has 6 pairs. My intention would be to install an access point in the shop to provide wifi for my smartphone and laptop.