Modular Dual Jack Extension LINE Cord Plug any 2 telecom device into the jack. Extends the length of the line cord 25'... Instructions: 1. plug into any wall jack. 2. Plug up to any 2 telecom device into the jack. Note: most homes are wired for 1 or 2 line service. For 3 lines,the home or office must be wired with 6 conductor or 8 conductor for 4 lines.