The easiest way to do this is open up excel, starting with a predefined area code, then using an algorithm to generate a series of random phone numbers (area + 7 digits). Say 50,000 phone numbers is then imported into a software to do automatic phone dialing loaded with a pre-recorded message. The odds are 25% - 50% of the time the generated numbers are valid, the valid numbers are then exported as a dataset for marketing/scamming purposes.