Make an iphone pay as you go?

I have Virgin Mobile right now and I don't really like it. I would like to get an Iphone but is there anyway to make that pay as you go? Like you just pay a certain amount every month with a card, like how Virgin Mobile is? I don;t want to spend more then 50$ a month on a phone bill so is there and phone carrier that offers that for the iphone? I would buy the Virgin Mobile version of it but its over 500$

Really depends on the iphone. The GSM (AT&T) can be used on a company called H2O wireless, they have monthly plans and pay as you go rates without any contracts. If it is unlocked, the AT&T iphone, you can use T-Mobile or Simple Mobile. Both are prepaid and require no contracts, both have monthly plans.