What I was unable to do with those boxes:
Make them register with a Quintum gatekeeper. They do not seems to be compatible.
Some people reported that they work perfect with GNUCK , the free gatekeeper that you download from the web.
I could not make it work on NAT configuration. Did not put much effort to the project also.
What I did: Make calls from box “a” on a fix I.P. to box “b” on another fix ip. No trouble ever.
Audio is perfect, almost no echo at all.(with a good I.P. route, around 200 ms round trip from U.S. to South America).
Good luck!!! I will be gone for two weeks, but we should be able to test after July 2nd.