There is a fairly common 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
Remember to return here, to 800notes.com, after you look at any of the information at that site, either to post more information, or to let us know you avoided the scam, or to read any further information about that number that others may post.