While the colors and PAIRS are documented on the web I often find these prewired systems to not be CAT5 or better. And sharing telco duty is well, more troubles to come.

So back to the web to see the wire assignments to the RJ 45 connections and hope for the best.

Here I use a simple cordless phone system in a fairly big 2 story home and WiFi. For one thing I got a powerline pair but later I upgraded my router and it's back to WiFi.