AT&T 874 - Manual (Page 11)

9
7 Plug the power adapter into a standard electrical outlet.
Convenience Port
: If you want to connect another device (such as
an answering machine or fax machine) to the wall jack, you can use
the jack on the phone labeled
AUX. This convenience port will
always use Line 2; a call picked up on Line 2 at another extension
may interrupt a fax, modem, or message transmission.
Convenience Port
INSTALLATION