WEB USER INTERFACE
V6: Identities - SIP(Section): Shared Line
V7: Identities - SIP Settings(Section):Shared Line
V8: Identities - SIP Settings(Section):Shared Line
PHONE USER INTERFACE
<user_shared_line idx="INDEX" perm="PERMISSIONFLAG">VALIDVALUE</user_shared_line>
If you have to share your extension (identity) with somebody else, this has to be enabled.