Can iPhone be used as a "prepaid" phone?

[maestrocasa]

I live in a place where cell-phone service is spotty, so I don't use my cell very much. As such, I have a "pre-paid" plan from ATT. (cut my monthly bill from an automatic $60 to less than $20!)

Would love to get an iPhone for some of its extra features, like compass, camera, microphone, etc., but have no interest in a high monthly cell plan.

can I just swap the SIM card from my current pre-paid phone and use it in the iPhone?

I figure I won't have all the 3G data access or visual voicemail with a pre-paid, but that's ok.

thanks!