Got same call on my cell that is on the "Do Not Call" list. Missed it. Called back and got the Not in Service message too.
This is how they are getting away with calling as they cannot be traced or reached in the end.

DO NOT PRESS ANY NUMBER! They will know it is an active phone and will call again or sell your # to others!
 Nov 30th, 2012
I just got a call as well and with the same message when I tried to call back. Wonder how they are getting around the national no call list. I am sure that my Governor's Office of Consumer Affairs will be interested in this.
 Nov 30th, 2012
They called my cell phone and I didnt answer. They left no message. Then when I called it back from my work phone the recording says that the number is not in service.
 Nov 30th, 2012
Just received a call from this number soliciting for help to lower or eliminate back taxes. You pressed "1" for help or "7" to be removed. I called the number back and got the "number not in service" message. Clearly a scam. Beware!
 Nov 30th, 2012