Didn’t you note by any chance that so far we are talking about A400 (first generation) ?
On the second generation Quintums, there is another trick.
In the special var_config.txt file yo u can specify the call signal port for H323:
This option will change the H225 call signalling port from 1720 to 1900.
Thus you can send calls to a Tenor where the 1720 port is blocked.