Polycom IP 650 - Manual (Page 39)

Customizing Your SoundPoint IP 650 SIP Phone
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Supporting Shared Lines
Your SoundPoint IP 650 SIP supports shared lines. A shared line is indicated
by a different line icon. In the following figure, the line 6721 is private and the
line 6723 is shared.
If two phones share a line, an incoming call to that number will cause both
phones to ring. The call can be answered on either phone but not both.
Calls on shared lines can be transferred, put on hold, or added to a conference.
Note Shared lines are an optional feature and may not be supported on your particular
system. For more information, contact your system administrator.
Note Call Forwarding is not available on shared lines.
Do Not Disturb (DND) on shared lines disables the ringing option only, the visual
indication is still in place.