Just got the same Nikki Johnson automated message and showed my attorney, he said it is a scam hands down.  The IRS is always a person and them are required by law to state their identification number when calling. Additionally, the IRS will send written notice to you and will not call your cell phone.

I received MULTIPLE calls from this telephone number, also from a Nikki Johnson. When I returned the call, it was clearly to a call center - I could hear a number of people in the background. "Agent Mike Walter," with a suspiciously not-Mike-Walter-like accent, asked for the phone number that had been called, and said that they were calling from the Criminal Investigation Division. Once I began asking questions, he hung up quickly.

Left threatening message on my elderly mother's answering machine.  Luckily, she asked me about it first and I could tell it was a scam.  It really scared her - these people should be prosecuted

Received same message, unreal and thank you all for reporting and commenting.  Now I cannot tell you what I will advise them if they should call back!!! I'll give them a taste if their own medicine.

i just got the same call.. on my cell phone.. i tried to call it back from my work phone ( i work for an attorney so the # probably showed up on caller ID) and someone picked up and hung.. so i called right back and got a man, when i wouldnt give him my cell phone # he called me a mother f**** r and hung up on me.. what a scam..