14.8.4.2.5. Three-Way Conferencing 
Conference scenarios are possible - CO behavior.
Display - On conference all parties located on OpenScape 4000 will
show correct display info for OpenScape 4000 conference members. Lync
Communications Server parties will be displayed as external parties.
Display won’t be updated on OpenScape 4000 if new members are added
at Lync Communications Server side.
Special Note:
Lync Communications Server side: Party C/OpenScape 4000 is added to
conference before party C is connected and invite/from is different to
basic call.
Display party C/OpenScape 4000 shows the configured (OpenScape 4000
system) trunk name.
OpenScape 4000 side: no message is sent towards Lync Communications
Server with "Conference" display update.