This number has called my parents home in Salt Lake City, Utah (area code 801) on the following dates and times:
1/9/2015 at 10:23am, 11:11am and 12:36pm  -- Caller ID:  530-870-4013
A few times on 1/10/2015  
And once on 1/6/2015 at 5:07 pm there was a call that they believe came from this number:  562-398-3823.

Here is what is said on the voicemail's they have left:  It is very bad English and very difficult to understand.

"Hi this message is intended contact you. My name Steve Martin.
I’m calling regarding an enforcement action executed by US Treasury, intending your serious attention.
Ignoring this will be an intentional second attempt to avoid initial appearance before a magistrate judge or a grand jury for a Federal criminal offense.  My number is 530-870-4013.  I repeat 530-870-4013.  I advise you to "call us" and help us to help you. Thank you."

"Call us" could have been "cooperate with us."

When I called the number to hear what it said on the other end, their are 5 rings followed by a recording.  Here is the message on the other end:

"The person at extension 9036 is unavailable. Please leave your message after the tone.  When done hang up or press the pound key. Sorry but the user's mailbox cannot accept more messages.  I'm sorry an error has occurred."  Call is then dropped from their end.

The IRS will always communicate by letter first.  If the matter is so serious that they need to communicate more directly they will send a letter by a courier and require a signature upon delivery.  They do not take people to court or involve a grand jury. Or generally send people to jail.  Of course those with serious tax evasion crimes are taken to court and are criminally prosecuted.  But I promise they would tell you more directly than a voicemail.