HP MFP Analog Fax Accessory 300 Fax Manual page 27

14 Reconnect all the cables, and turn on the MFP.
Reconnecting the cables
Figure 1-24
When connecting the fax accessory to a phone line, ensure that the
Note
phone line being used for the fax accessory is a dedicated line that is
not used by any other devices. Also, this line should be an analog line
because the fax will not function correctly if it is connected to some
digital PBX systems. If you are not sure whether you have an analog
or digital phone line, contact your telecom provider.
HP recommends using the phone cord that comes with the fax
Note
accessory to ensure that the accessory functions correctly.
ENWW
Installing the fax accessory 19