AT&T E3813B - Manual (Page 14)

11
Telephone operation
Options while on calls
Multiple handset use
While on a call, a person on the
ringing destination handset can press
PHONE
/FLASH
or SPEAKER to join
the conversation.
The person on either handset can press
OFF
/CLEAR
, or place the handset in
the telephone base or charger to drop
out of the call, but the call will not be
terminated until all handsets hang up.
NOTE: A maximum of two handsets can be
used on an outside call, and the other two
handsets can be used on an intercom call.