Brother MFC-5440CN User Manual page 167

_ lf You Do Not Subscribe to Distinctive Ring Service:
You must plug your TAD into the EXT. jack of your MFC. If your
TAD is plugged into a wall jack, both your MFC and the TAD will
try to control the phone line. (See illustration below.)
Unless you are using Distinctive Ring, do not connect a
TAD elsewhere on the same phone line.
TAD
TAD
When you are using a TAD, the LCD shows Telephone.
A-11 APPENDIXA