Something seems very strange about your Localphone VM problem. While I can certainly imagine a problem with the U-Verse RG that corrupts a SIP CANCEL request and causes an unanswered call to continue to ring her phone, that should have nothing to do with Localphone's sending the caller to voicemail. If the caller continued to hear ringing, IMO that had to be a problem with the Localphone configuration or with their service. As I mentioned earlier, the setting for voicemail-on-no-answer is in an obscure place (Internet Phone -> Call Forwarding). Can you retest if that is working now?
I am reasonably certain that Localphone does not route calls differently based on IP address, so moving the OBi overseas won't change anything. However, they may route a call differently based on the caller's number, because of various tariffs related to intra- vs. inter-state and intra- vs. inter-LATA. Also, it's possible that if the general problem with FL routing is fixed, the special 4-digit prefix may be discontinued or repurposed. So, you should be prepared to adjust the OBi configuration if needed. That should not be hard to do, either through the OBiTalk portal, directly via port forwarding, or by remote access to her desktop and running a browser from there.