Did not answer.  Left a voicemail...automated message saying they were the IRS and it was a "final notice" and that they were filing a lawsuit against me. Not buying it. Taxes are paid and besides, IRS would probably send letters, not call with an automated message.

Scam IRS lawsuit call. SCAM!

Received call from 617-944-1397 saying The IRS is bringing a lawsuit against me, call back number was 901-663-4599. Scam?

Advisory:
You may have been exposed to a variation of scam #11, as described here:

http://phonehelp.2truth.com/facts.html

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BEWARE!  Its a scammer calling you!The IRS doesn't initiate contact with taxpayers by email, text messages or social media channels to request personal or financial information. In addition, IRS does not threaten taxpayers with lawsuits, imprisonment or other enforcement action. Recognizing these telltale signs of a phishing or tax scam could save you from becoming a victim.
See: How to know it’s really the IRS calling or knocking on your door