This is not a "crank" call or someone with too much time on there hands. These are very malicious phishing scams, I would advise if you get these calls report it to your service provide and they will normally block the number from there network.
If you listen carefully, they say they are from "internal revenue serviceS" (as opposed to the Internal Revenue Service) so maybe they are covering themselves by not exactly using the actual IRS name. Anyway, hopefully they'll get a karmic 'reward' for their evil behavior.
Received call from 674 166 5748 at 08:27am message left said IRS suing. Call 206 201 2799 for more info. Knew it had to be a scam. Did not find info on Google for # called from.
Message on voice mail. "This is the IRS and we are filing a lawsuit against you." My thoughts are bring it on big boy and I will own your fraudulent company. Scam