Googled the number while it was ringing, and it didn't show up so I answered it. It was a lovely computerized voice telling me the IRS is about to file a lawsuit against me, and asking me to call back on that number.
It looks like I'm the first to put them on 800Notes, but I'm sure I won't be the last...
I got the same voice message with a lovely robot voice on 7/14. They filed a lawsuit against me without sending me a letter?? Glad to find the posts here.