At the end of last week, I got this call from the "IRS" claiming I owed money and could be subject to a lawsuit or even arrested, leaving a very threatening sounding voice mail.
I've seen this in the news so I knew right away. Don't fall victim to this because they can and will sound "real".
Here's the official word from the actual IRS:
http://www.irs.gov/uac/Newsroom/Scam-Phone-Calls-Continue;-IRS-Identifies-Five-Easy-Ways-to-Spot-Suspicious-Calls