Iphone 4 Application Help!!!?

I owe an Iphone 4. I was just exploring AppStore to download an app called "Hidden". Its used to hide photos and Videos. It was a paid app (1.99 $) n i clicked on buy app, coz i thought i'll purchase it via my card, but i realised it didnt ask for any card no or anything, n simply downloaded.... What will happen now? Will the cost be cut from my Sim card ( i owe a prepaid vodaphone sim), or should i keep on downloading paid apps for free.....??? Reply asap n be serious..... My Iphone's not jailbroken.... Thnks guys....