I've been getting a couple calls where a recorded voice says that the IRS has a warrant for my arrest and I need to talk to them to settle up my back taxes. If you get one of these, HANG UP. The IRS does not work this way - if they want to communicate with you, they send you a letter via snail mail.
These are like the Nigerian Prince, only via telephone (almost certainly Voice over IP, or VOIP, which lets them call from pretty much anywhere in the world toll free). Just hang up if you get one of these nuisance calls.