AT&T DEFINITY Communications System Generic 1 User Manual page 7

The various components which appear on the bottom of the 8520T voice/data
terminal are shown in Figure 2 and explained below.
Adjunct jack
Handset jack
Line jack
Used for connecting an external speakerphone, a
headset adaptor, or other adjunct equipment. The jack
is labeled "ADJUNCT."
WARNING: Do not insert the handset cord into the
"ADJUNCT" jack. It will cause equipment damage.
Used for connecting the handset cord to your voice/data
terminal. The jack is labeled
Used for connecting the line cord to your voice/data
terminal. The jack is labeled "LINE."
.
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