There isn’t much difference between an Ethernet cable and your in-house telephone wire (the RJ-11 jack that your phones use even plugs into most RJ-45 Ethernet ports, albeit on 4 wires instead of 8).

My house has a bunch of telephone jacks (around 8?) and they are all home-run directly to the telco box outside the house. I'd like to place my voip adapter in the basement and use it to power all of ...