I got the same call 2 minutes ago. I did call back. Rang 1 time, a foreigner answered. The IRS never answers the phone right away, and they usually are not foreign
I just got the call while I was filling up with gas. It creeps you out! No one wants to tangle with the IRS, because you will lose. The cards are stacked against you.
Official IRS Government site detailing this scam and providing links to report it:
http://www.irs.gov/uac/Newsroom/IRS-Warns-of-Pervasive-Telephone-Scam