I have had a couple of these calls. Called back on a non identifiable line assuming it was a scam call. I had to let the phone ring a long time (10 rings) and the ring was very strange (broken ring) as if it was being routed to another place. A woman answered and there was lots of noise in the background as if she was at a pay phone or sitting in a call center with lots of people talking. I didn't talk to her but she identified herself as IRS.
Total scam. See my entry .IRS does not initiate contacts by phone. IRS does NOT file lawsuits. It has enough administrative authority by statute and regulations to collect all lawful federal taxes . The scam originates in India and Pakistan. Ignore and block the calls.
Got a call from this number on my iPhone this morning and the initial caller ID read "Egypt", I ignored it and they left a voicemail. The voicemail was listed from Washing D.C., with the same "IRS lawsuit" automated message. Another addition to my blocked caller list!