I work in the telecom industry: blocking the number won't do anything, they can set the ANI (caller id info) to anything they want. They can make it random everytime they call you if they wanted to. They are probably terminating from a different country over SIP after finding some insecure SIP PBX servers which are all over the place. The absolute best thing you can do is let them get a disconnected signal or ring no answer enough times so they take you off their list. Every time you answer they take note of the date/time and resell that information to other marketers/scammers so they know what time and day of week to get ahold of you. Don't ever answer a number you don't recognize. If you don't recognize it let it go to voicemail, if they explain who they are add them to your contacts and call them back, otherwise continue to ignore them, and block if it gives you peace of mind. That simple.
Hang up, as well. Perhaps they call, judge whether the person sounds a certain way (i.e. elderly, uneducated, etc.), then make a decision whether to pursue their scam. Next time one of you are in Ellensburg, WA... feel free to pay these guys a visit.