Both of my Vonage routers are on my RV082 DMZ interface and each has its own static public IP address (no cascaded NAT problems). FYI, I was already using the max 9600 baud rate, no compression, no error correction, no handshaking, and a DSL filter on the modem output tricks.
Also, as I said in the review update, normal VoIP voice service and incoming faxes continue to work with no problems.
Interestingly, I tried sending and receiving between my Vonage fax line and my RingCentral fax line today, and it worked perfectly in both directions. I had in fact done a couple of fax tests right after I got the new Comcast service activated, and those tests also worked OK (but they were local calls to a neighbor). However, since I had two failures in as many days to two different long distance locations (I was able to return those faxes using my new RingCentral line which would eliminate any failure on the remote end as the cause of the failure), I will no longer be able to trust using Vonage fax over my Comcast connection as my only fax service. Of course, those fax transmissions might have failed using an AT&T DSL connection too, but I have no way to verify or test that anymore.
For now, I am keeping the Vonage fax line active along with the RingCentral line (with the RingCentral line now being published as my official fax line). After a couple of months, after I am reasonably sure that there are no gotchas with the RingCentral service, and that nobody is sending me any faxes on the Vonage line, I will probably either drop the Vonage fax line, or just convert it to a backup voice line.
As a bonus, using the RingCentral line will actually cost less than using the Vonage fax line , so I really don't mind switching. The base price is the same, but the RingCentral service does not have the added bogus fees that Vonage attaches (my Vonage $9.99 fax line actually costs me $14.85 per month with the added bogus fees).
