The U.S. Federal Trade Commission (FTC) handed down new regulations for sending pre-recorded phone messages on August 19, 2008, that will two things. First, by December 2008, all automated phone broadcasts will be required to include a key or voice activated opt-out feature. And second, by September 2009, all callers will need the "prior express WRITTEN agreement of the recipient to receive such calls." Having an "existing prior business relationship" will be no longer sufficient to send automated phone calls.
The only exceptions to the new rules will be health care related calls subject to HIPPA (Health Insurance Portability and Accountability Act of 1996), charitable fundraising calls make to non-profit members or those who have previously donated, and political calls.
You can see a report and learn more about the details here.