It is not posible to talk from a Quintum or Cisco to a Clarent GATEWAY directly.
The only way for a Clarent gateway to talk to a non-Clarent equipment is trough a “gatekeeper”.
That is really a gatekeeper/converter, since allow a Clarent to H323 conversion.
You end calls from your Quintum to the Clarent gatekeeper, without registering to it. Just sending the H323 call as with any other H323 gateway.
I do have my Quintum setup normal, no modifications whatsoever, just plain h323 quintum, and I send calls to a Cisco 5300 and a Clarent at the same time.
Hope that the information helps!