There's quite a few fields in SS7 not accessible via SIP, one of which should indicate whether or not the call was originated internationally or not. Whether o

There's quite a few fields in SS7 not accessible via SIP, one of which should indicate whether or not the call was originated internationally or not. Whether or not a call with domestic looking CPN from an international location will be accepted is up to the switches handling it, but they're designed to successfully complete a call in almost any possible circumstance. It's possible that the international gateway might rewrite the CPN field with something else, but I doubt they'd go as far as refusing to let it through. The screen parameter within SS7 details whether or not the CPN field has been defined by the end user. Most SIP users won't have access to this either, but the vast majority of calls from them (but not from other sources) will look like the number is user provided. For that reason, some voicemail systems that've historically let you log in automatically just by setting your CPN to the subscriber number have started to only let you do that when the screen parameter is set to network provided.