Mine rang once also - however, I read about a scam where people hit call back and it goes to an offshore account that then bills you hundreds of dollars for "services". Basic rule, if was important, the would leave a message.
Phone rang once and I answered it. Got a message to "not hang up, you have been referred by a friend". I hung up and blocked the number. Problem is, have about 1/2 dozen blocked calls and all have had the same message, but each time, a different phone number with a different area code has been used. Not sure how they can do this, but my guess is that despite different phone numbers, they all belong to the same company. This is undoubtedly a scam of some sort.