Brother MFC-5440CN - Manual (Page 169)

A - 13 APPENDIX A
Special line considerations
Roll over phone lines
A roll over phone system is a group of two or more separate
telephone lines that pass incoming calls to each other if they are
busy. The calls are usually passed down or “rolled over” to the next
available phone line in a preset order.
Your MFC can work in a roll over system as long as it is the last
number in the sequence, so the call cannot roll away. Do not put the
MFC on any of the other numbers; when the other lines are busy and
a second fax call is received, the fax call would be transferred to a
line that does not have a fax machine. Your MFC will work best on
a dedicated line.
Two-line phone system
A two-line phone system is nothing more than two separate phone
numbers on the same wall outlet. The two phone numbers can be on
separate jacks (RJ11) or combined into one jack (RJ14). Your MFC
must be plugged into an RJ11 jack. RJ11 and RJ14 jacks may be
equal in size and appearance and both may contain four wires
(black, red, green, yellow). To test the type of jack, plug in a two-line
phone and see if it can access both lines. If it can, you must separate
the line for your MFC. (See Easy Receive on page 4-4.)