This article explains how to turn off Remote RX on the PIXMA MX472 / MX479.
Solution
Turn Off Remote RX
If the fax continues to interrupt telephone conversations after the Remote RX ID number was changed, turn off Remote RX. The default setting from the factory is ON. See the following steps to turn off Remote RX.
Make sure that the printer is turned on.
Press the Setup button.
The Setup menu screen is displayed.
Use the button to select Fax settings, then press the OK button.
Use the button to select Adv. FAX settings, then press the OK button.
Use the button to select Remote RX, then press the OK button.
Use the button to ON, then press the OK button.
To disable Remote RX, select OFF.
Use the buttons or select a Remote RX ID between 00 - 99, then press the OK button.
Press the FAX button to return to standby mode.
Note
The * (asterisk) on the LCD indicates the current setting.