Brother MFC-5440CN - Manual (Page 170)

APPENDIX A A - 14
Converting telephone wall outlets
There are three ways to convert to an RJ11 jack. The first two ways
may require assistance from the telephone company. You can
change the wall outlets from one RJ14 jack to two RJ11 jacks. Or,
you can have an RJ11 wall outlet installed and slave or jump one of
the phone numbers to it.
The third way is the easiest: Buy a triplex adapter. You can plug a
triplex adapter into an RJ14 outlet. It separates the wires into two
separate RJ11 jacks (Line 1, Line 2) and a third RJ14 jack (Lines 1
and 2). If your MFC is on Line 1, plug the MFC into L1 of the triplex
adapter. If your MFC is on Line 2, plug it into L2 of the triple adapter.
RJ14
RJ11
RJ14
Triplex Adapter