Its the IRS scam, and its all over this board. It has even made the national news. The scammer demands immediate payment of over due taxes. They must be payed by wiring the money or by giving the scammer your credit card or bank account number. The scammer threatens you with arrest.
The IRS never makes initial contact by phone. They never demand immediate payment. The caller is a scammer. Do not send him any money. Report him to the real IRS.
I just got the same message and I called back. He said that he wanted to talk with my attorney and when I told him that I don't have an attorney, he hung up. I happen to be an attorney and so I doubt that the call is real.