I'm looking for a way of generating numbers into my database. Just like http://us.battle.net/wow/en/, I need a way of entering a million numbers into my database so that when someone wants to participate in my site activities, he/she will need to purchase a recharge card similar to the above website.

Another e.g is the phone recharge card, does anyone know how they did their stuff i.e how their database or recharge card works. Your response is needed. Thank you.