Sharp UX-P400 - Manual (Page 46)

Auto-Cordless Fax Control (answering with an extension phone in TEL mode)
44
1
Answer the extension phone when it
rings.
2
If you hear a soft fax tone, wait until your fax responds (the extension
phone will go dead), then hang up.
3
If the fax doesn't respond, or if the other party first talks to you and then
wants to send a fax, press once and twice on the extension
phone (only on a tone dial phone). This signals the fax to begin
reception. Hang up.
•
The above step is necessary if you have set the Fax Signal Receive setting
(see below) to NO.
•
Your fax will not accept the signal to begin reception (5**) if a document is
loaded in its feeder.
5
Phone goes dead
Beep