I am not looking to throw blame/shade or other about how the hostname came to be nor did I. Perhaps I went overboard in my explanation, but I was not certain that you were understanding my response to thinking a firmware fix would not likely correct the scenario as described. Further, it is not nor ever was a question of whether or not I agree with the Skyswitch method. I never made a remark of liking it or not; only that they must be trying to provide security. .It is their method and I have no qualms with it, only curiosity as others may elect to use their service in the future and may pose the same question.
There was never a diversion of any kind from the main issue. You feel it is a firmware issue as you are comparing one device against another. We have no pcap files from either to compare nor settings, just that one does and the other does not and again, assuming all is equal.
However, I was going to, and apparently am, **_suggesting trying DNS SRV and then NAPTR SRV in the GXW DNS_settings ** as I am guessing the YS is set to SRV… if you want to fully check the device compatibility. I have a hunch that this will resolve the issue as I am guessing the provider is using SRV records. I may be wrong, but it may be worth a shot in an effort to use the preferred GXW.
As far as FXS gateway manufacturers, there was no mention of what a vendor recommended, you only indicated, " there appears to be only 3 manufacturers that sell FXS ATA’s". Not knowing the reasons or limitation associated to the comment, I provided a list of others, many of which I have touched at one time or another as you had complained of the web issue with the YS model and seemed to be looking for others.
If I offended in some way, then I am sorry for that. It was not my intent. If you do elect to try the SRV settings in the GXW, I would be interested to know the outcome.