There is a fairly new IRS scam that is brazen enough to leave a message when you are unavailable to answer the call. The scammers state that the IRS is filing a lawsuit against you, and leaves a number for you to return the call. Please remember that the IRS will never demand immediate payment over the phone, nor will they require that you use a specific payment method to pay your taxes.
The sheriff of Dodge County Wisconsin, Dale Schmidt, recently received this phony IRS call. Upon calling the number, the operator on the other end admittted he was working in Afghanistan, and that the call was indeed a scam. You can listen to the call and read more about this case here.