They called my cell phone twice but I was in a meeting at work so didn't answer.  I didn't call back because I am pretty sure the IRS sends out notices in the US mail.
They said the issue was serious and the Internal Revenue was starting prosecution against me.

I received a call on my answering machine right before Christmas from allegedly the IRS.  She said:  "We want you to call us back at your very first hearing of the message as this issue is very serious.  T here is a notice filed against you by the IRS officer, so before things go worse against you call us back at on our hotline Visa 7037911755. I repeat it 7037911755. Don't disregard this message and return the call.  Remember delay calling us back about this matter will aline you and put a legal prosecution on your name.  So we hope you justify this matter as quickly as possible."