I was still living in Vancouver, Canada when I learned maybe six or so years ago AT&T has removed all roaming restrictions in North America. So a few of us banded together, one of us crossed over to New York picked up a group subscription of sorts and we had very cheap subscriptions. Only the last 1-2 years did Canadian providers caught up, somewhat.
But the real advantage was if anyone called from a "local" number, local to my SIM at least, I immediately knew it was spam. I do not know anyone in Buffalo, I do not do business in Buffalo, there's no authority which has anything to do with me there, nothing. It's spam.