Above should be applicable to the SPIP335 as I am not aware of this phone having a dedicated Softkey for DND.
For the new VVX500/600/300/400 series this is at present not applicable and requires a Feature request via your Polycom reseller in conjunction with a Polycom sales engineer.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services
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