Idea

If an inbound call comes into RingCentral through an external circuit which presents a caller ID which matches a number of any RingCentral customer, this is known to fraudulent.  If that number 'belongs' to RingCentral, the call would come from an internal RingCentral circuit, not one of the external circuits.  Therefor since we know the caller ID is fraudulent, we can safely block it.  This would improve the experience for all your customer and reduce bandwidth cost on your circuits.