Can I turn my old iPhone 3G into a pre-paid phone?
Question: I have an older iPhone 3G and my contract with AT&T is up this month. I'm going to buy a new iPhone 4S for myself but is there a way to convert the 3G into a pre-paid iPhone? That'd be ideal for my high school daughter because she'd have a preset limit that she can pay for herself. Is this possible?
Answer: The iPhone 3G or 3GS uses regular-sized sim cards that you can find in pay-as-you-go phones, like AT&T’s GoPhone.
In fact, you can convert your iPhone to a pre-paid phone plan by simply buying a cheap $25 or $30 GoPhone, taking out it's sim card and swapping it into the iPhone.
Once you have the GoPhone sim card in the iPhone you can use it just like any other prepaid phone and make all the calls you want.