Brother FAX-2440C User Manual page 184

_ lf You Do Not Subscribe to Distinctive Ring Service:
You must plug your TAD into the EXT. jack of your machine. If
your TAD is plugged into a wall jack, both your machine and the
TAD will try to control the phone line. (See illustration below.)
Q Unless you are using Distinctive Ring, do not connect a
TAD elsewhere on the same phone line.
TAD
When you are using a TAD, the LCD shows Ext. Tel in Use.
APPENDIX A A-12