These campaigns are paid for by the National Republican Congressional Committee (NRCC) and have occurred in at least Illinois, New York, and New Hampshire. They've been partially stopped in New Hampshire after intervention by the state Attorney General--but only by discontinuing calls to voters on the national Do Not Call list.
One of the New York calls can be heard here (WAV file).
UPDATE: Here's a list of the twenty districts where these calls are occurring and which Democrats they are attacking. They're in California, Illinois, Florida, New York, Virginia, Kentucky, Georgia, Iowa, North Carolina, Connecticut, Kansas, New Hampshire, Wisconsin, and Pennsylvania.
UPDATE: The Democratic Congressional Campaign Committee has sent the National Republican Congressional Committee a cease and desist letter.
UPDATE (November 7, 2006): The New York Times and the Washington Post have covered the story. Michigan Representatives Conyers and Dingell have asked Attorney General Alberto Gonzales to investigate the issue.