DO NOT CALL THEM BACK! This is how the "one-ring scam" works (from ScammersUncovered dot com): First you’ll receive a phone call from an unknown number. True to their name, they’ll ring once and hang up. If you call the number back, you’ll be put through to an international number who will charge you premium rates, and drain all of the dollars from your account. You won’t find out exactly how much has been charged, until your phone bill knocks the wind out of your sails.
The easiest way to prevent scam callers is by being aware of them. Never answer calls from unidentified numbers. If you want to know who called you, use a Reverse Phone Lookup to safely identify unknown callers. Only when you know that the caller is someone you can trust, answer or give them a call back.
Most of these scumbags are offshore, so good luck trying to get any justice after the fact. The US Do Not Call Registry means nothing to them, unfortunately. The best thing you can do is to be wary of unknown phone callers. Always, ALWAYS use a reverse lookup when the number ends up in your phone log. If it’s an important call, the caller will leave a message — and even then, be wary.
Have had a bazillion scam calls, and have NEVER heard of ANYONE who has had problems with being charged for bogus high rate calls (seems to be a myth that gets bandied about). If someone was charged for such calls, why in the heck would they pay? In order to end up with problems, you have to give out your credit card number to unknown callers.