I would suggest that you have not set the EthernetInterface External NAT IP setting on the Quintum. Tenors use this setting for the IP addresses embedded in the H.225.0 messages; mainly for negotiation of audio channels through fast start.
If your Quintum is using a private IP address with its fast start elements, then results will depend on which carrier you use.
The ITSP I work for (DUAL Talk) will detect that private IP addresses have been used, and will replace these with the real IP address of the caller. Other companies will try to send the audio to the private IP address. This will fail, and result in no audio being received from the carrier.
There is more information at http://www.quintum.com/support/xplatform/network/Tenor-Firewall-NAT.pdf.