BOAC,
Your wording is confusing.
If all you want to do is run a telephone extension from your master socket in which you can plug in another telephone, you can do that either by running a simple telephone extension or if you want to be more future proof technically, just look up the concept of structured cabling using CAT5/CAT6 cable and then use a balun to give you the socket for the phone (not as complicated as it sounds).