"Internal Revenue ServiceS"--note the s they use in their robo-scam call. The IRS doesn't play this game, so just delete the message and their supposed threat. Ooooooo, I'm terrified.
I got the same message, in fact, several times in the last few days, on my home phone and my cell phone. I have a neighbor who works for the IRS and she has assured me that this is a scam. IRS will always contact you by letter.