Samsung SF-5800P - Manual (Page 17)

Extension Phone
If you want to use a regular phone or answering machine with your
machine, connect the phone into the EXT.LINE jack.
Plug the cord of your extension phone or answering machine into the
socket marked EXT.LINE on the back of the machine.
TEL LINE
EXT. LINE
1.8
Set Up Your Machine
Telephone Line
Plug one end of the telephone line cord into the TEL LINE jack and
the other end into a standard phone wall jack.
TEL LINE
EXT. LINE