Siemens 600Series - Manual (Page 128)

6-4 ROLMphone 300/600 Series User Guide
Automatic Privacy
If your telephone has been assigned the Automatic Privacy feature, no
one can bridge (or join) your calls unless you turn off the feature.
To turn off Auto-
matic Privacy ➩ During a call, press the Privacy key, or
press TRANSFR and dial # # 2.