Claiming to be IRS and a warrant has been issued

It's a scam.  They use MAGIC JACK from computers in India and Pakistan to call you.  The IRS would send you a registered letter if they were going to sue you.

See the IRS website for more:

http://www.irs.gov/uac/Newsroom/IRS-Warns-of-Pervasive-Telephone-Scam