Just bought an iphone, i want a pay as you go plan?

I just bought an iphone too use as an ipod. But now i have some money and i want to get a pay as you go plan.
Here is what i need:
~Able to bring in my own phone
~Pay as you go (no contract)
~And it has to be able to support an Iphone4

I bought the phone on amazon and now i want to use it as an actual phone c: I can't get a contract/monthly plan because i have no idea if i will have the money every month or not c: Thank you:** <3

Added (1). Sorry if thats confusing the iphone i got was indeed the iphone4. I apologize (i only said to support an iphone because i looked at metropcs and they won't take a iphone… )

Att gophone plans.$35 and up

It makes no sense what you just wrote, you bought an Iphone but you want it to be able to support an Iphone 4? What does that even mean? Did you buy an Ipod thinking you could make calls on it?

Oh and if you wan a pay as you go thing, you have to have an unlocked Iphone or take it to a carrier store to have it unlocked.