This is absolutely a scam.  I work for a CPA and we have had several clients get these calls and this morning (Saturday) I received one.  I did not answer but, got the same basic message.  Do not call back and or give them ANY information at all.  The IRS NEVER calls people with issues, only mails notices and such.  Report and then ignore.  

Received call this afternoon (Nov. 8) from (415) 234-9482.  Did not answer but they left message.  Voice was male with Indian accent indicating we owed the IRS.  We owe nothing to the IRS and have no debts.  This is clearly a scam.  We will not call back as they requested.  A real nuisance and a totally unprofessional and amateur scammer with Indian accent..

what a scam I cant understand why this is going on! Thank god I am smarter than this.

Got a call this afternoon from 415-234-9482 Michael Carter posing as an IRS agent citing
case number 549634 they were investigating me and I had to make arrangements to pay.
I was concerned that this might be one of those numbers you would respond to and they
would keep you on the line as long as possible to 'discuss your case' and your phone bill
would be charged $1000. a minute or some such nonsense --

same here. received mechanical message to return the call and not to  disregard the phone message or else.  I called the phone # back and a lady answered "IRS"!!!   when I asked who was calling - she hung up.