1738 does not pick up, caller gets odd busy signal when machine is not full

SOURCE: 1738 att answ machine-need to change message

Record Your Announcement
Before using this answering system, you
should record the announcement (up to
three minutes long) that callers will hear
when the system answers a call. If you
choose not to record an announcement,
the system answers with a pre-recorded
announcement: “HELLO. PLEASE LEAVE A
MESSAGE AFTER THE TONE.”
1 Press and hold a. When the
system beeps, speak toward the
microphone normally, from about nine
inches away. While you are recording,
the Message Window blinks .
To stop recording, release a.
The system automatically plays back
your announcement.
To review your announcement, press
and release a.
To erase your announcement and
return to the pre-recorded announcement,
press Dwhile your announcement is
playing.
Callers can skip the announcement by
pressing #.

SOURCE: callers get busy signal, all 3 phones say

Possible causes:
1. Another phone is off-hook besides these 3.
2. Bad house wiring - call the phone company.
3. Bad wiring somewhere between your house and the Central Office - call the phone company.