John. Its a scam number from what I have found. They call claiming to be the IRS and saying they are suing then you only get the busy tone when you call back. From what I understand is you can report the number at the IRS website. I received a call from them today and did some researching to figure out what was going on and this Is what I was able to find so I hope it helps

I got this EXACT same message today and when I tried to actually call the IRS to see what the heck this message is about, I can't get a real live person to answer the phone.  I called the number back that claimed the IRS is going to sue me, and it's busy and then rings and then they hang up.....I am hoping this is a scam?:??

There is a widespread IRS or "tax scam" being  practiced by scammers on both Canadian and USA residents.
USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.

Educational post:
This scam is also described as scam #11, here:
http://phonehelp.2truth.com/facts_rev.html

If you were contacted by an IRS impostor, you may file a report, after clicking on this link:
http://www.treasury.gov/tigta/contact_report_scam.shtml

Thank for the info cuz they keep calling me too

If you call the number that called you and wait you will get some guy with an Indian accent. He answers IRS but when you try to get him to answer some specific questions he hangs up.