The IRS scammers have a new number to try to trick you. Use your Caller ID, don't answer any call you don't recognize or use your answering machine. This one actually leaves a message... don't fall for it. The IRS will never call with this type of notice.
I highly recommend recording your phone message to saying something like, "...we screen all of our calls...so, if we don't recognize your number we're never going to answer... but... you're welcome to leave a message..."