Usually done by syndicate.

If the contest involve having a chance to win by SMS if your transaction code is xxxx number then:

- get lots of people that have the bank's cc
- wait at tesco or other Hypermarket cashiers
- offer to pay for groceries then collect cash. Offer 5 to 10% discounts
- collect transaction codes and register for entries

True story, I know the friend of the friend who know that guy. He borrowed the car for wedding from the friend