Thanks for the pointer, Steve. I have an Arris DG1660A router (new in recent weeks, so probably the cause of the issue). However, disabling SIP ALG did not change the behavior. I'll have to try the setting in Obitalk expert configuration and see if that helps.
Edit: disabling X_DiscoverPublicAddress did appear to fix the issue. The only oddity now is that when I call the Callcentric test number 17771234567 I get a State Farm voice menu. I don't remember it doing that before, but it's been years since I used it.
If there are additional settings on the Arris that might help, I'd prefer to fix the issue that way, so if you have further recommendations I'd appreciate it.