I received a call from this number but I did not answer. I received a voice mail that had a recording of a woman's voice saying that this was the final notice of the IRS' lawsuit against me. They asked that I contact them immediately at 206-201-2799. I figured this was a scam because nothing about this call seems right.

Total scam.  Originates in either India or Pakistan.  
See:  http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Report them:
http://www.treasury.gov/tigta/contact_report_scam_ok.shtml

IRS does not file lawsuits.   Court action, if any is handled by the DOJ and all parties are entitled to legal assistance if it is a criminal matter.  But--tax disputes are for the most part civil matters.  90% of all IRS tax disputes are settled administratively.  IRS has absolutely no authority to call on local law enforcement for anything. Local law is never involved in IRS tax disputes.   If LE is necessary, US Marshals do the job.  IRS does not cold call anyone and ask for money. No one is prosecuted for ordinary tax disputes.  All determinations of tax liability are subject to appeals.  All  contacts by the IRS are initiated by US mail.

These idiots left a message on my answering machine telling me that they were from the IRS, and that
they were suing me and this was my last chance to pay up.

The number they left to call back was 202-239-2835.

I called them back, and asked in kind of a mock inquisitive tone, "Is this the IRS". The guy immediately knew
I was on to them and very sheepishly replied "yes". I then asked him how much money I owed, he
started f bombing me and hung up.  

Just now got a call from this number with the same voicemail as described above "this is the IRS.. final notice.. lawsuit.."

I haven't investigated but I'm more than confident that this is a Scam with a capital S. I'm not worried about it. If the IRS wanted me they would send a letter.