The person says they are with the Treasury Department and if you call them back they try to threaten you with different things. They are definitely foreigners from Central Asia or Middle East.
You're right, not the IRS! I heard that scams are going around right now, and to beware that the IRS will always contact by mail first, and when they start calling it actually says IRS on the caller ID. We've been contacted by the IRS before and it's not some spooky computer voice. Yikes!
"... you received this message. I need you or your retained attorney of records to return the call. The issue at hand is extremely time-sensitive. My phone number is 213-289-3844. Do not disregard this message, and do return the call. Now if you don't return the call, and I don't hear from your attorney either, then the only thing I can do is wish you a good luck as the situation totally unfolds on you. Goodbye."
Computerized voice quality was on par with the speech synthesizer I had on my TI-99 4/A in the early 80s.