Callers are located in India and Pakistan and they ignore all US laws. There's nothing the US can do and the local governments do little.
Invest in a call blocker and DO NOT pick up on call numbers you do not recognize. Common scam, been around for years.
I too like to mess around with these idiots. The IRS does absolutely nothing, I reapeat that ABSOLUTELY NOTHING by phone. It is alwyas be registered mail. I asked them for their IRS badge number, nothing, I told them I was contacting the states attorney, they laughed. I finaly told them I was an FBI agent and that their building was surrounded: silence and then a lot of screaming and then "click"... HA!!