It's a land line from Tampa, Florida. The claim is that you've won a trip and they make it appear very legit. Then they ask you for your credit card number to pay some BS $450 fee. I enter contests often, including online. The key is to use a junk email addy that you don't mind being filled with crap, and of course never divulge sensitive information by email or on the phone. You should never have to pay upfront to receive a prize.
I received 2 calls per day last friday and this monday. 3 different number all beginning with the same numbers but I'm quite sure there are all related; Here are they :813-968-5601; 813-968-5690; 813-968-5642.
As Blade, I've made the mistake of entering a contest on-line the day before has occured the first call.