‘One Ring’ Phone Scam
One-ring calls may appear to be from phone numbers somewhere in the United States, including three initial digits that resemble U.S. area codes. If you call any such number, you risk being connected to a phone number outside the U.S. Variations of this scam rely on phony voice-mail messages urging you to call a number with an unfamiliar area code to “collect a prize” or to notify you about a “sick” relative.
Source: www.fcc.gov