Police say people have lost hundreds of thousands of dollars.
The caller claims the person has won the lottery and/or a car and must pay a transfer fee to collect the winnings. Victims are sometimes instructed to buy prepaid money cards at a local store and told how much to load onto the card.
Police say legitimate sweepstakes don't require winners to pay to collect. They recommend people never wire money or provide personal information, such as bank account numbers or Social Security numbers, to a stranger.
People should contact a phone provider, local police or the Federal Trade Commission if they suspect a scam.