The PRI was able to dial internationally before (according to the customer), so I am operating under the assumption that it is our equipment until proven otherwise. AT&T have done 'tests' but have come up with no faults.
No, I have not tried that change yet. I will give it an attempt and report back.
Sadly, I am working this issue remotely. My POC is very hard to pin down, but when I get hold of him I will ask.
Thank you!