Check out the following article. It states that over 200,000 voice phishing/vishing calls into Korea, from other countries, were blocked in January and February. Some additional statistics are given as well that break the calls down by type, bank, etc. Most of them are imitating Korean banks. Unfortunately, there isn't any information about how these calls are blocked, I presumably by Korean service providers.
It seems like US-based service providers could do the same thing - block international calls claiming to be US-based finanical institutions. This isn't trivial though, you need technology at the right location in your network and managing blacklists of numbers takes a ton of work (I know, we do it too).