are rj9 and rj11 the same size?
RJ11 is an older version of RJ12, and they are the same size. ... RJ12 is backwards compatible with RJ11, but RJ11 will not work with RJ12. Coiled handset cords use a smaller connector called RJ9 or RJ22 (both names refer to the same thing). These are physically smaller than RJ11/RJ12 and use four conductors.