These calls are not coming from the IRS or anywhere else in the US government.
Here is a story from FOX 13, Tampa Bay, Florida about these calls. It's the best explanation I've found so far of these calls as well as what to do when you receive one and to whom to report the call and how:
This an India or Pakistan based IRS scam. Do not fall for this.
Read http://www.treasury.gov/tigta/press/press_tigta-2014-03.htm
The IRS does not initiate any legal action over the phone. Report it also to your local law enforcement agency. The scammers use magicjack (Ymax corporation) voice over IP lines. This is against this company's terms of use and can lead to termination of their contract. However only law enforcement can initiate the contact with Ymax. Ultimately this is a case for the FBI legal attache in Delhi or Islamabad. If you are really annoyed call or write to your representative in Congress. As these scams happen all over the country maybe this will trigger a reaction (and the NSA can finally be a force for good).
The guy with a heavy accent left a similar message on our voice mail. He said to call Jim Arthur as soon as we get the message. He called today, Friday, approximately at 7:30 p.m. I did not have any doubt that it is a scam.
Received a voice mail on the phone from Special Agent Jim Arthur, Badge #1593 regarding some kind of an assault. The guy has a very heavy accent and said he was with the FBI and it was an urgent call and to please call back,