Claims to be the last call to me from the IRS concerning a lawsuit against me? It's also a recording using a formal sounding women's voice.
Get a busy signal if I try to a them call back. Seems like a scam? The IRS  usually has recordings and they normally send notices only in the mail?

Yes it's a scam. A very common one, unfortunately. Phone calls made through internet connections (VOIP) are virtually untraceable, so naturally criminals are having a field day with the situation. They fake the Caller ID (which is why you can't call them back – the y probably used a number that isn't in service for their spoofed Caller ID) and it's pretty much imposibkle to nab them. Especially if they're overseas, as many of them are.