"IRS has filed suit against you".  Seems like this scam should be vulnerable, since the call-in number actually has to connect to the scammers.

They spoof local numbers.  Use VOIP or Magic Jack phones.  Or burn phones.  No way the numbers can be traced and even if the callers  could be found, what could be done.  Nothing. They are located in India and Pakistan.  US can' t do anything and the local governments do little.   INvest in a call blocker and do NOT pick up on numbers you do not recognize.

My elderly parents also received a call from the "IRS' stating there is a suit against them. I told them not to worry that the IRS do not call you for something like this. Total scam and it is pissing me off that they go after seniors to rip them off!!!