This is the OPD-DIR review of 
    A SIP Response Code for Unwanted Calls
    draft-ietf-sipcore-status-unwanted-04
which defines a new SIP response that allows called
parties to indicate this decision to SIP entities.

Summary: Ready

Operationally, the new code (666) should be treated 
with the same disposition as any 6xx code, and SIP devices
should destroy the session transaction. SIP devices 
which support the 666 code MAY perform other actions
as described (in future), but no actions are mandatory.
There is one requirement in the Security Considerations:
   ...the response code SHOULD NOT be used for creating
   global call filters unless the calling party identity has been
   authenticated using [I-D.ietf-stir-rfc4474bis] as being assigned to
   the caller placing the unwanted call.

Operators and their suppliers should check/test their
SIP systems to ensure that a 666 response is handled
as any 6xx should, before deployment. 
(this point could be added, if seen as useful)