I got a call today from the same number and they left a partial pre-recorded voice message. I called them back with my phone number blocked and they refused to identify themselves until I called with the number unblocked. Appears to be, as others have stated, an IRS scam. Doing a little research, I found out that the Treasury Department is treating this as a serious matter and they have set up a yellow highlighted block near the top of their website to report it. Go to https://www.treasury.gov/tigta/
Received message, same as above, called back. I chucked when he said "IRS", and he said, "That's right. Its not the IRS. This is a scam. We just shooting Mother F*ckers".
Received call today regarding tax fraud and we should "kindly" call this number 407 547 1001 before arrested of complaint is sent to federal tax commission. I forwarded a complaint form to ic3.gov (FBI cyber crime unit per advice from AT&T).