3
titled “Removing the Telephone Tray” in the Installation section of this 
guide.
10) Redial button — For redialing the last number that you dialed using the 
dial pad.
11) Speaker button — For accessing the Speaker feature. This feature can be 
used for 
listening only
. If you want to speak to the other party, you must use the 
handset.
Note:  With the Group Listen feature, you can activate the speaker while you 
are using the handset, and both can be active at the same time.
12) Handset — A handset is provided for placing and receiving calls. In most 
cases, you must lift the handset (go off-hook) before you can use a feature.
Headsets
Headsets for 6400 Series telephones allow one-touch hands-free operation. 
To answer a call, press   and then the dial pad key on which the 
Headset feature is administered. (For more information on using   and 
the dial pad keys to access features, see “Voice Features” later in this 
manual.)To disconnect, press   again and then the dial pad key on 
which the Headset feature is administered. 
Headsets consist of a headpiece (1 in Figure 2 below) and modular base unit 
(2). The base unit plugs into the Handset jack (3).
FIGURE 2 The Headset Attached to a 6400 Series Telephone
Feature
Feature
Feature
7
321
4
*
56
89
O#
Volume
1
2
3