Upon seeing missed calls from unfamiliar numbers on our cell phones or home phones, we often instinctively call the number back to see who it was. According to a recent warning issued by the Better Business Bureau, however, that quick call-back can end up costing consumers ridiculous sums of money.

A fairly new scam called the “one-ring phone scam” has become increasingly popular of late and is costing people a lot of money. It involves perpetrators setting up computers that call thousands of random numbers, let the phone ring once, and then hang up. When people call the number back, they are billed a $20 international call fee and then connected to a paid premium service, such as an adult chat line that charge $9 per minute or more.

According to the BBB, calls typically originate from area codes outside of the U.S., such as Antigua or Barbuda (area code 268), the Dominican Republic (809), Jamaica (876), British Virgin Islands (284) or Grenada (473).

“Better Business Bureau recommends if you don’t recognize an out-of-state telephone number on your caller ID, ignore it and if you do answer, do not call back,” the group said in a news release. “Also you should check your cell phone bills carefully and inform your carrier if you spot any unauthorized charges. The earlier you document the fraud, the better your chances of having some or all of the charges removed.”

Bottom line: if someone who calls but misses you has something important to say, he or she will leave a voicemail or text you. If her or she doesn’t leave a message, there’s no reason to call back.